Self-perceived lactose intolerance results in lower intakes of calcium and dairy foods and is associated with hypertension and diabetes in adults1-4
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Self-perceived lactose intolerance results in lower intakes of calcium
and dairy foods and is associated with hypertension and diabetes
in adults1–4
Theresa A Nicklas, Haiyan Qu, Sheryl O Hughes, Mengying He, Sara E Wagner, Herman R Foushee, and
Richard M Shewchuk
ABSTRACT 2010 National Institutes of Health Consensus Development
Background: Self-perceived lactose intolerance may result in ad- Conference on Lactose Intolerance and Health concluded that the
verse dietary modifications; thus, more studies are needed to un- true prevalence of lactose intolerance in the United States is not
derstand the prevalence of self-perceived lactose intolerance and known because studies have varied in their interpretation of what
how it relates to calcium intake and selected health conditions. constitutes this condition, and many studies assessed individuals
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Objective: The objective was to examine the effects of self- without a diagnosis of clinical lactose intolerance (4).
perceived lactose intolerance as it relates to calcium intake and Several reviews have summarized earlier studies on lactose
specific health problems that have been attributed to reduced intakes maldigestion and estimated that lactose intolerance in Americans
of calcium and dairy foods in a nationally representative multiethnic occurs in ’15% of whites, 50% of Hispanics, and 80% of Af-
sample of adults. rican Americans (6–8). This is in stark contrast with a recently
Design: This was a cross-sectional study in a national sample of published study in the Journal of the National Medical Asso-
3452 adults. The relation between self-perceived lactose intoler- ciation and first mentioned in the Consensus report of the Na-
ance, calcium intakes, and physician-diagnosed health conditions tional Medical Association on the role of dairy and dairy
was analyzed by using linear regression analyses. nutrients in the diet of African Americans (9, 10). According to
Results: Of the total sample, 12.3% of respondents perceived them- this research, only 24% of African Americans surveyed actually
selves to be lactose intolerant. The age-adjusted prevalence of self- reported being lactose intolerant. In another study that assessed
perceived lactose intolerance was 7.8% for non-Hispanic whites, prevalence estimates for adults who reported themselves to
20.1% for non-Hispanic blacks, and 8.8% for Hispanics. Respondents be lactose intolerant, 8%, 20%, and 10% of whites, African
with self-perceived lactose intolerance had significantly lower (P ,
Americans, and Hispanics self-reported being lactose intolerant,
0.05) average daily calcium intakes from dairy foods than did those
respectively (11).
without self-perceived lactose intolerance. A significantly higher
(P , 0.05) percentage of respondents with self-perceived lactose
1
intolerance than of respondents without self-perceived lactose intol- From the US Department of Agriculture/Agricultural Research Service,
erance reported having physician-diagnosed diabetes and hyperten- Children’s Nutrition Research Center, Baylor College of Medicine, Houston,
sion. The odds of self-reported physician-diagnosed diabetes or TX (TAN and SOH); the Survey Research Unit, Center for the Study of
hypertension decreased by factors of 0.70 and 0.60, respectively, Community Health, University of Alabama at Birmingham (HQ); the De-
for a 1000-mg increase in calcium intake from dairy foods per day. partment of Health Services Administration, University of Alabama at Bir-
mingham, Birmingham, AL (MH); the Survey Research Unit, Center for the
Conclusions: Self-perceived lactose-intolerant respondents had
Study of Community Health, University of Alabama at Birmingham, Bir-
a significantly lower calcium intake from dairy foods and reported
mingham, AL (SEW and HRF); and the Department of Health Services
having a significantly higher rate of physician-diagnosed diabetes Administration, University of Alabama at Birmingham, Birmingham, AL
and hypertension. Am J Clin Nutr 2011;94:191–8. (RMS).
2
This work is a publication of the USDA/Agricultural Research Service
Nutrition Research Center, Department of Pediatrics, Baylor College of
INTRODUCTION
Medicine (Houston, TX). The contents of this publication do not necessarily
Lactose intolerance refers to the gastrointestinal discomfort reflect the views of policies of the USDA, nor does the mention of trade
that may be experienced with lactose maldigestion—a condition names, commercial products, or organizations imply endorsement from the
resulting in incomplete digestion of lactose (1, 2). Lactose US government.
3
maldigestion occurs when more lactose is consumed than the Supported by the Dairy Research Institute and USDA/Agricultural Re-
existing lactase enzyme can hydrolyze at one time. Clinical search Service specific cooperative agreement 58-6250-6-003.
4
Address correspondence to TA Nicklas, USDA/Agricultural Research
lactose intolerance refers to a physician’s diagnosis of lactose
Service Children’s Nutrition Research Center at Baylor College of Medicine,
intolerance after diagnostic testing for lactose maldigestion with Department of Pediatrics, 1100 Bates Avenue, Houston, TX 77030. E-mail:
the use of methods such as the breath-hydrogen test (considered tnicklas@bcm.edu.
the “gold standard” for this diagnosis) or the stool acidity test Received December 21, 2010. Accepted for publication April 7, 2011.
(3–5). Whereas lactose intolerance exists in the United States, the First published online April 27, 2011; doi: 10.3945/ajcn.110.009860.
Am J Clin Nutr 2011;94:191–8. Printed in USA. Ó 2011 American Society for Nutrition 191192 NICKLAS ET AL
Reported prevalence rates of lactose intolerance are in- differentials that may exist among group members or between the
consistent, partly because the concept of lactose intolerance is group members and the moderator. Because the NGT tends to
poorly defined. For example, research indicates that a portion of promote even rates of participation across respondents, the input
individuals who report or perceive themselves as having lactose from group members is equally weighted and the data generated
intolerance are not lactose maldigesters, so the cause of their by this process are considered a valid representation of the views
gastrointestinal discomfort is not related to lactose (4). Indi- of the group (35).
viduals who have self-perceived lactose intolerance, regardless of Respondents for the NGT sessions were recruited by racial-
whether they were self-diagnosed or physician diagnosed, tend to ethnic groups. A total of 8 NGT sessions were conducted with 6
avoid dairy foods (10, 12, 13). Avoidance of dairy foods may lead to 8 adults per session. The information provided by the par-
to nutrient shortcomings that could predispose them to adverse ticipants from each racial-ethnic groups was combined as an
health outcomes, including poor bone health (14–16), higher exhaustive list and subjected to a thorough distillation process.
blood pressure (17–21), higher body weight (22–25), a higher The response distillation used to develop inclusive lists of lac-
incidence of colon cancer (26–28), and a higher risk of de- tose intolerance perceptions and facilitative strategies involved
veloping diabetes (29–33). Therefore, the goal of this study was compiling and aggregating the prioritized, substantively similar
to examine the association between self-perceived lactose in- responses across the racial-ethnic groups. Any nonredundant
tolerance, calcium intake, and specific health problems that have responses endorsed by any group were also included in gener-
been attributed to a reduced intake of calcium and dairy foods in ating lists of perceptions of lactose intolerance and facilitative
a nationally representative multiethnic sample of adults. strategies among adults. An overinclusive pool of survey items
was formulated from the responses. These items were then
SUBJECTS AND METHODS
reviewed by an expert panel with extensive understanding of the
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literature to finalize the survey.
A survey was developed from information derived from
Nominal Group Technique (NGT) meetings. Random digit di-
aling was used to administer the survey (interview format) to Final questionnaire
a nationally representative multiethnic sample of adult respond- The questionnaire survey consisted of 4 or 5 distinct sections
ents. The study was approved by the Institutional Review Boards depending on self-perceived lactose intolerance. For those res-
for Human Use at the University of Alabama at Birmingham and pondents who do not self-identify as lactose intolerant, the survey
Baylor College of Medicine. included 1) screening questions to identify lactose intolerance,
2) a calcium intake section, 3) demographic data, and 4) self-
Respondents reported physician-diagnosed health conditions. For those self-
perceived lactose-intolerant respondents, the set of surveys
Respondents were 19–70-y-old adults from 3 racial-ethnic included 1) screening questions to identify lactose intolerance,
groups (whites, African Americans, and Hispanic Americans). 2) a calcium intake section, 3) facilitative strategies and per-
For the qualitative phase, adults aged 30–50 y who perceived ceptions, 4) demographic data, and 5) self-reported physician-
themselves to be lactose intolerant (defined to participants as diagnosed health conditions.
digestive problems that occur when consuming milk or dairy
products) were recruited through a current database at the
Children’s Nutrition Research Center (CNRC) (n ’ 100). For the Calcium intake
quantitative phase, respondents were recruited and assessments A food-frequency questionnaire (FFQ) developed by Sebring
were conducted through random digit dialing at the University et al (36) was used to assess the calcium and dairy intakes of study
of Alabama at Birmingham (UAB) Center for the Study of respondents (available in English and Spanish). This FFQ is a list
Community Health. A person was classified as having lactose of 25 foods, including dairy products; beverages; combination
intolerance if he or she responded yes to the question “Do you foods, such as lasagna, macaroni and cheese, and pizza; vege-
think that you are lactose intolerant?” after a brief description of tables, grains, and nuts; and other foods and was validated in
the condition was provided. People who responded no or don’t a sample of 341 adults against a 7-d food record (36). Dairy
know were classified as not lactose intolerant. Exclusion criteria products included milk (white or chocolate) to drink, milk on
included gastrointestinal surgery, cow milk allergy (defined to cereal, instant breakfast drinks made with milk, yogurt, pudding,
participants as causing symptoms such as wheezing, nausea, ice cream, calcium-fortified drinks and juices, cheese, and cot-
headache, stomachache, itchy hives—with most reactions hap- tage cheese. The beverages included cocoa, café latte, café au lait,
pening for ,1 d), antibiotic therapy within the past 2 mo, or and cappuccino; combination foods included a wide variety of
intercurrent illness, such as inflammatory bowel disease. foods made with milk or cheese. Specific to this study we looked
at total calcium intake, servings of dairy products consumed, and
Nominal Group Technique the contribution of dairy products to calcium intake. Other
sources of calcium designed for lactose-intolerant consumers
The approach to developing the questionnaire was driven by were also included, such as calcium supplements and lactose-free
consumer-oriented phenomenology and reflected the belief that products.
questionnaires should be designed by systematically incorpo-
rating the views of those for whom the measure was intended. The
NGT is a formal “brainstorming” or idea-generating technique Administration of the questionnaire
developed by Delbecq et al (34). Unlike the traditional focus The questionnaire was interviewer administrated by using
group, the structured framework of the NGT minimizes power Computer Assisted Telephone Interviewing (CATI) techniques.SELF-PERCEIVED LACTOSE INTOLERANCE 193
Interviewers who were trained in proper interviewing procedures, 2.5th percentile (ie, 214.29 mg/d) or above the 97.5th percentile
study specific protocols, and human subjects’ protection con- (ie, 3192.14 mg/d) were eliminated from the analyses. The ex-
ducted the interviews. Interviewers were monitored and super- clusion of persons in the bottom and top 2.5th percentiles was
vised for quality control. The sample frame consisted of all based on a tentative decision to minimize the effects of extreme
households in the contiguous United States with a telephone, and implausible self-perceived levels of calcium intake from
including both landlines and cell phones. The sample was strat- foods. On the basis of the trimmed means, no statistically sig-
ified by race-ethnicity into 3 mutually exclusive racial-ethnic nificant difference was found between those who perceived
groups. A nationally representative sample of randomly gener- themselves to be lactose intolerant and those who did not with
ated telephone numbers was purchased from a commercial respect to the percentages of respondents excluded from the
sample provider. A nationally representative sample of randomly analyses. Moreover, the differences in average calcium intakes
selected telephone numbers were called from the Survey Re- between those with and without self-perceived lactose intolerance
search Unit’s CATI facility at the University of Alabama at were consistent, irrespective of the inclusion or exclusion of the
Birmingham. Sampling frames were obtained by the Survey outlier values. The final sample consisted of 3452 respondents,
Research Unit, which is part of the standardized procedure they which included 1071 male and 2381 female respondents. In terms
use for this kind of research. The sample was divided into 3 strata: of racial-ethnic groups, 1648 were non-Hispanic whites, 958 were
census tracts with 50% African Americans, census tracts with non-Hispanic blacks, and 846 were Hispanics. The mean (6SD)
50% Hispanic Americans, and all remaining census tracts. age of the respondents was 48.71 6 13.16 y. Of the total sample,
Calls were placed to all numbers to locate households with el- 12.3% of respondents had self-perceived lactose intolerance. The
igible respondents. age-adjusted prevalence rate of self-perceived lactose intolerance
Spanish interviewers were conducted by bilingual interviewers was 7.8% for non-Hispanic whites, 20.1% for non-Hispanic
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using a questionnaire translated into Spanish. Interviewing began blacks, and 8.8% for Hispanics (Table 1).
in January and was completed in October 2009. Numbers were No statistically significant difference between respondents
called up to 15 times, including day, evening, and weekend calls. with self-perceived lactose intolerance and those without self-
Final disposition codes were assigned to all numbers based on perceived lactose intolerance was found with respect to age
CDC Behavioral Risk Factor Surveillance Survey disposition (Table 2). A statistically significant sex difference was found
code guidelines, which can be located at www.cdc.gov/BRFSS/ between respondents with self-perceived lactose intolerance and
technical_infodata/pdf/2003DQRHandbook.pdf. The average time those without self-perceived lactose intolerance, ie, significantly
taken to complete the surveys was 13 min. Interviewers were more women than men reported self-perceived lactose into-
supervised at all times and randomly electronically monitored lerance (P , 0.05). A statistically significant difference in the
a minimum of 4 times/mo. No problems were encountered. The percentages of self-perceived lactose intolerance among racial-
cooperation rate, calculated as the number of completions divided ethnic groups was found, ie, significantly more non-Hispanic
by the number of completions + refusals + surveys terminated in black than non-Hispanic white and Hispanic respondents re-
process, was 35.1%. The overall response rate, calculated as the ported self-perceived lactose intolerance (P , 0.05). However,
number of completions divided by the completions + refusals + the percentages of self-perceived lactose intolerance were sim-
assumed eligible after unable to reach after 15 attempts + lan- ilar for non-Hispanic whites and Hispanics (P . 0.05).
guage barrier + surveys terminated in process, was 25.3%. Respondents with self-perceived lactose intolerance had sig-
nificantly lower (P , 0.05) average daily calcium intakes from
dairy foods than did those without self-perceived lactose in-
Data analyses tolerance, but there was no statistically significant difference in
Chi-square tests were used to examine the association between calcium intakes from nondairy foods between those with and
self-perceived lactose intolerance and the respondents’ age without self-perceived lactose intolerance (Table 3 and Table
group, sex, and race-ethnicity group. Separate linear regression 4). Men had significantly lower average daily calcium intakes
analyses were conducted to examine the relations between cal- from dairy foods than did women (P , 0.05). Relative to non-
cium intakes from dairy and nondairy foods as predicted by self- Hispanic white respondents, both non-Hispanic blacks and His-
perceived lactose intolerance, sex, and age by using Predictive panics had significantly lower average daily calcium intakes from
Analytics SoftWare (SPSS Inc, Chicago, IL) 18.0. Logistic re- dairy foods and significantly higher average daily calcium intakes
gression analyses were conducted to examine the relation between from nondairy foods. Generally, aging was significantly associ-
self-reported physician-diagnosed diabetes and hypertension and ated with declining daily calcium intakes from both dairy and
calcium intakes from dairy foods and calcium intakes from foods nondairy foods (Table 4).
by using Mplus 6.1. The logistic regression model included the Differences in self-reported physician-diagnosed health con-
predictors calcium intake from dairy and nondairy foods, sex, and ditions were also noted between respondents with and without
race-ethnicity and self-reported physician-diagnosed hypertension self-perceived lactose intolerance (Table 5). A significantly higher
and diabetes as the outcomes. Calcium intake was expressed in percentage of respondents with than without self-perceived lac-
1000-mg units. tose intolerance reported having physician-diagnosed diabetes
and hypertension. Daily calcium intakes from dairy foods were
statistically associated with both self-reported physician-
RESULTS diagnosed diabetes and hypertension (P , 0.05). The odds of
The total sample size was 3729. Ninety-four individuals who self-reported physician-diagnosed diabetes or hypertension de-
had missing values of self-perceived lactose intolerance and 183 creased by factors of 0.70 and 0.60, respectively, for a 1000-mg
individuals with a daily calcium intake from foods below the increase in calcium intake from dairy foods per day, after control194 NICKLAS ET AL
TABLE 1
Estimates of self-perceived lactose intolerance prevalence by race-ethnicity and sex (n = 3630)1
Subjects with
Population Population Sample self-perceived Crude Age-adjusted
Race and sex estimate proportion size lactose intolerance prevalence2 prevalence rate3
% n n % %
Non-Hispanic
whites
Male 77,426,611 49.80 591 38 6.43 6.76
Female 78,044,109 50.20 1113 94 8.45 8.45
Total 155,470,720 100.00 1704 132 7.75 7.75
Non-Hispanic
blacks
Male 11,610,914 46.97 269 46 17.1 16.98
Female 13,109,217 53.03 766 183 23.89 20.96
Total 24,720,131 100.00 1035 229 22.13 20.05
Hispanics
Male 14,704,497 52.38 273 23 8.42 7.62
Female 13,367,230 47.62 618 64 10.36 9.32
Total 28,071,727 100.00 891 87 9.76 8.81
Total
Male 103,742,022 49.81 1133 107 9.44 9.62
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Female 104,520,556 50.19 2497 341 13.66 12.48
Total 208,262,578 100.00 3630 448 12.34 11.55
1
Age-adjusted prevalence and population estimates were calculated on the basis of data from the US Census Bureau,
2005–2007 American Community Survey: http://www.census.gov/acs/www/index.html.
2
Crude prevalence = (no. ofXpeople with self-perceived lactose intolerance/no. of people in survey) · 100%.
3
Age-adjusted prevalence = (no. of people in an age group/total population) · (no. of people with self-perceived
lactose intolerance in an age group/no. of people in survey in an age group) · 100%.
for other variables in the model. The odds of self-reported sample, 12.3% of respondents perceived themselves to be lactose
physician-diagnosed diabetes increased by a factor of 2.21 for intolerant, and the age-adjusted prevalence rates of self-perceived
non-Hispanic blacks relative to non-Hispanic whites, after con- lactose intolerance were 7.8% for whites, 20.1% for African
trol for other variables in the model. The odds of self-reported Americans, and 8.8% for Hispanics. These estimates are nearly
physician-diagnosed hypertension increased by a factor of 1.79 identical to those previously reported in 1084 respondents (11).
for non-Hispanic blacks relative to non-Hispanics whites, after
control for other variables in the model (P , 0.01). The odds of
TABLE 2
self-reported physician-diagnosed diabetes increased by a factor Percentages of self-perceived lactose intolerance by age groups, sex,
of 1.14 for Hispanics relative to non-Hispanic whites, after and race1
control for other variables in the model (P , 0.05). The odds of
self-reported physician-diagnosed hypertension increased by Self-perceived
lactose intolerance
a factor of 0.70 for Hispanics relative to non-Hispanic whites,
after control for other variables in the model (P , 0.01). Sex and Yes No Total
daily calcium intake from nondairy foods were not associated (n = 419) (n = 3033) (n = 3452)
with self-reported physician-diagnosed diabetes and hyperten-
sion (P . 0.05) (Table 6). n % n % n %
Differences were noted between respondents with and without Age
self-perceived lactose intolerance with respect to the average 39 y 95 22.67 770 25.39 865 25.06
number of weekly servings of milk related foods (data not 40–49 y 117 27.92 675 22.26 792 22.94
shown). Respondents with self-perceived lactose intolerance 50–59 y 112 26.73 848 27.96 960 27.81
consumed significantly less (P , 0.05) milk, yogurt, soup made 60 y 95 22.67 740 24.40 835 24.19
with milk, pudding made with milk, cheese, cottage cheese, and Sex*
ice cream than respondents who did not report self-perceived Male 100 23.87 971 32.01 1071 31.03
Female 319 76.13 2062 67.99 2381 68.97
lactose intolerance.
Race*
Non-Hispanic white 127 30.31 1521 50.15 1648 47.74
Non-Hispanic black 210 50.12 748 24.66 958 27.75
DISCUSSION Hispanic 82 19.57 764 25.19 846 24.51
The results from this national survey confirm that the preva- Total 419 100.00 3033 100.00 3452 100.00
lence of self-perceived lactose intolerance is significantly lower 1
Excludes cases with missing values for self-perceived lactose intoler-
than prevalence estimates of lactose intolerance based on lactose- ance and cases with values in the bottom 2.5 percentile or top 2.5 percentile
maldigestion studies summarized in reviews (6–8). Of the total for calcium intake from both dairy and nondairy foods. * Overall P , 0.01.SELF-PERCEIVED LACTOSE INTOLERANCE 195
TABLE 3
Mean daily calcium intakes from dairy and nondairy foods by age group, sex, and race for respondents with and without
self-perceived lactose intolerance (n = 3452)1
Self-perceived lactose intolerance
Variable Yes (n = 419) No (n = 3033) Total (n = 3452)
mg
Daily calcium intake from dairy food
Age
39 y 431 6 263 645 6 378 622 6 373
40–49 y 416 6 274 617 6 348 588 6 345
50–59 y 370 6 215 575 6 335 551 6 330
60 y 403 6 284 538 6 302 523 6 303
Sex
Male 393 6 274 569 6 348 553 6 346
Female 408 6 255 605 6 341 578 6 338
Race
Non-Hispanic whites 468 6 268 655 6 360 641 6 358
Non-Hispanic blacks 351 6 249 468 6 288 442 6 284
Hispanics 442 6 247 593 6 327 579 6 323
Total 404 6 260 593 6 344 570 6 340
Daily calcium intake from nondairy food and beverages
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Age
39 y 652 6 420 676 6 458 673 6 454
40–49 y 574 6 428 629 6 458 621 6 454
50–59 y 556 6 382 556 6 412 556 6 409
60 y 529 6 392 541 6 412 539 6 410
Sex
Male 596 6 398 601 6 446 601 6 449
Female 570 6 410 598 6 434 594 6 437
Race
Non-Hispanic whites 523 6 357 532 6 405 531 6 401
Non-Hispanic blacks 561 6 423 616 6 429 604 6 428
Hispanics 670 6 417 715 6 482 713 6 476
Total 577 6 407 599 6 438 596 6 434
1
All values are means 6 SDs. The table includes descriptive data that were used in the analyses for Table 4 to
determine significant differences.
The crude prevalence of self-perceived lactose intolerance in whites, 50% of Mexican Americans, and 80% of non-Hispanic
non-Hispanic blacks (22.1%) is consistent with the research blacks (6–8). The results from this study indicate that the previous
highlighted originally in the National Medical Association prevalence rates for lactose intolerance may have been grossly
Census Report and again in a recent study (9, 10). However, these overestimated from maldigestion studies.
prevalence rates are significantly lower than previous estimates ex- A possible explanation for this disparity is that the maldi-
trapolated from lactose-maldigestion tests: 15% of non-Hispanic gestion studies using a breath-hydrogen test administered a
TABLE 4
Regression analysis summary for self-perceived lactose intolerance predicting daily calcium intake from dairy foods1
Daily calcium intake from dairy foods Daily calcium intake from nondairy foods
Unstandardized Standardized Unstandardized Standardized
coefficients coefficients coefficients coefficients
B SE b B SE b
Constant 738.02 14.11 594.40 18.60
Self-perceived lactose intolerance 2150.51 17.18** 20.14 231.16 22.66 20.02
Males (females as reference) 249.98 11.98** 20.07 8.04 15.80 0.01
Non-Hispanic blacks (non-Hispanic whites as reference) 2189.70 13.44** 20.20 70.53 17.72** 0.07
Hispanics (non-Hispanic whites as reference) 282.02 13.94** 20.10 164.38 18.39** 0.16
Age, 40s (age 40 y as reference) 238.15 16.02* 20.05 233.15 21.13 20.03
Age, 50s (age 40 y as reference) 283.03 15.33** 20.11 291.81 20.21** 20.09
Age, 60s (age 40-y as reference) 2121.36 15.98** 20.15 298.54 21.07** 20.10
1
R2 = 0.10 (dairy), R2 = 0.04 (nondairy; n = 3452, P , 0.01). *P , 0.05, **P , 0.01.196 NICKLAS ET AL
TABLE 5
Descriptive characteristics of predictors for self-reported physician-diagnosed diabetes and hypertension1
Diabetes (n = 3445) Hypertension (n = 3442)
Yes No Chi-square Yes No Chi-square
Variable (n = 453) (n = 2992) or t test (n = 1143) (n = 2299) or t test
Self-perceived lactose intolerance (%) 16.56 11.43 9.76* 16.01 10.22 23.98**
Women (%) 71.52 68.58 1.59 69.38 68.73 0.15
Men (%) 28.48 31.42 1.59 30.62 31.27 0.15
Non-Hispanic whites (%) 34.44 49.77 37.05** 43.83 49.72 10.60**
Non-Hispanic blacks (%) 41.94 25.64 52.15** 38.67 22.44 100.07**
Hispanics (%) 23.62 24.60 0.20 17.50 27.84 44.25**
Daily calcium intake from dairy foods (mg) 511 579 4.32** 516 598 6.97**
Daily calcium intake from nondairy foods (mg) 578 434 0.95 565 611 3.02*
1
Chi-square test used for sex and race; t test used for calcium intake variables. *P ,0.05, **P ,0.01.
challenge dose of 50 g lactose in water, which is not comparable body weight (22–25), and a lower incidence of colon cancer (26–
with a serving of dairy food typically consumed with a meal (4, 28). Some studies (29–33) have also linked dairy food intake or
6, 37). The likelihood that an individual experiences symptoms its nutrients with a lower risk of developing diabetes. Individuals
of lactose intolerance after consuming 12 g lactose [eg, 1 cup who avoid dairy products may find it difficult to meet adequate
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(’237 mL) milk] with a meal is much lower than that after intakes of calcium and magnesium from other food sources alone
consuming an amount of lactose that is 4.5 times (equivalent to (43), which may have detrimental health effects throughout life.
a quart of milk) that in a single solution of water. Thus, prev- One study found that adolescent girls who perceived themselves
alence rates of lactose maldigestion do not necessarily equate to be milk intolerant had significantly lower milk and calcium
with prevalence rates of lactose intolerance because individuals intakes and a lower bone mineral content of the spine (12). Of
with lactose maldigestion may or may not experience the gas- interest, ’50% of the girls who perceived themselves to be milk
trointestinal disturbances associated with lactose intolerance. In intolerant were not lactose maldigesters. In the current study,
addition, health care professionals have no standardized method total calcium intake was significantly lower in those respondents
of diagnosis (38). who reported self-perceived lactose intolerance than in those
In this study, no significant difference in self-perceived lactose who did not, particularly calcium intake from dairy foods (eg,
intolerance with age was found. However, more women and non- milk, yogurt, and cheese). The lower calcium intake from dairy
Hispanic blacks had self-perceived lactose intolerance. Although foods was not compensated for with a higher intake of calcium
previous studies and reviews have reported that non-Hispanic from nondairy foods.
blacks are more likely to report having lactose intolerance (6, 9, In addition to this nutritional shortfall, a larger percentage
10), it is unclear at this time why women have a higher prevalence of respondents with than without self-perceived lactose intolerance
of self-perceived lactose intolerance and it warrants further study. self-reported having physician-diagnosed diabetes and/or hyper-
Individuals with self-perceived lactose intolerance may tension. Furthermore, a larger percentage of those with lower
eliminate or decrease their intake of dairy foods. The dairy food calcium intakes from dairy foods also reported having physician-
group is an important contributor of many nutrients lacking in diagnosed diabetes and/or hypertension, which suggests that
American’s diets, including calcium, potassium, and vitamin D the higher prevalence of these conditions among those with
(39), and limiting dairy food intake may have adverse health self-perceived lactose intolerance may be associated with the
effects. Studies have shown that intake of dairy foods or dairy lower dairy calcium intake. Although research has linked dairy
nutrients is associated with a higher diet quality (40–42), im- food and calcium intakes to a reduced risk of osteoporosis and
proved bone health (14–16), lower blood pressure (17–21) and colon cancer, this study found no differences in physician-
TABLE 6
Summary of logistic regression analyses predicting diabetes and hypertension diagnoses (n = 3436)1
Diabetes Hypertension
Variable2 B SE Wald statistic Odds ratio B SE Wald statistic Odds ratio
Daily calcium intake from dairy foods 20.36 0.17 22.06* 0.70 20.51 0.12 24.20** 0.60
Daily calcium intake from nondairy foods 20.11 0.13 20.89 0.89 20.14 0.09 21.50 0.87
Sex 20.09 0.12 20.76 0.92 20.01 0.08 20.10 0.99
Non-Hispanic blacks 0.79 0.12 6.45** 2.21 0.58 0.09 6.60** 1.79
Hispanics 0.32 0.14 2.32* 1.14 20.35 0.10 23.54** 0.70
1
Daily calcium intake from dairy foods and daily calcium intake from nondairy foods were coded as 1 unit = 1000 mg Ca/d. Akaike information
criterion = 6872.16, Bayesian information criterion = 6945.87, sample size–adjusted Bayesian information criterion = 6907.74. *P , 0.05, **P , 0.01.
2
Sex coded as 0 = females, 1 = males; non-Hispanic blacks coded as 0 = not non-Hispanic blacks, 1 = non-Hispanic blacks; and Hispanics coded as 0 =
not Hispanics, 1 = Hispanics.SELF-PERCEIVED LACTOSE INTOLERANCE 197
diagnosed osteoporosis and colon cancer. This may have been relative calcium intake or to help identify individuals who may be at
a result of the way in which these conditions are diagnosed. Unlike risk of low calcium intakes. As such, the mean intake reported in this
a typical blood pressure test during an office visit or a blood study is not consistent with national averages showing that Ameri-
glucose measurement during a conventional laboratory test, di- cans, on average, are not meeting adequate intakes of calcium (43).
agnoses for both osteoporosis and colon cancer require specific
We thank Nisha Jamal for help in preparing the manuscript and Bee Wong
nonroutine tests that are not commonly conducted during ordinary for obtaining research articles.
medical examinations. Thus, it may be entirely possible that an The authors’ responsibilities were as follows—TAN and RMS: conceptu-
association does exist for these conditions but that it was not alized the study and conducted all of the data analyses; TAN: wrote the first
detected because the study relied on reporting of a physician’s draft of the Introduction and Discussion; RMS, MH, HQ, and HRF: wrote the
diagnosis and not on objective diagnostic testing of each condition. Subjects and Methods and Results; and TAN: substantially revised the man-
This study has important implications. Health professionals uscript with critical feedback from the other authors. All authors: reviewed the
need to be aware that fewer people experience the symptoms of data and read and approved the manuscript. The funding sources had no input
in the design, implementation, analyses, or interpretation of the research.
lactose intolerance than previous estimates indicate, and the self-
None of the authors had a potential conflict of interest.
perception of lactose intolerance may have a detrimental effect on
nutrient intake and health outcomes. As a result, health pro-
fessionals need to focus on definitively determining the source of
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