Amount of Daily Protein Intake Is Not Associated with Skeletal Muscle Strength in Older Adults
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pISSN: 1229-6538 eISSN: 2383-5699
ORIGINAL
Korean J Clin Geri 2021;22(1):40-46
ARTICLE https://doi.org/10.15656/kjcg.2021.22.1.40
Amount of Daily Protein Intake Is Not Associated
with Skeletal Muscle Strength in Older Adults
Ha-Na Kim , Sang-Wook Song
Department of Family Medicine, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea, Seoul, Korea
Background: A reduction in skeletal muscle strength is independently related to physical disability and mortality and skeletal
muscle strength predicts these outcomes in older adults. However, few studies have investigated the influence of protein con-
sumption on skeletal muscle strength in older adults. Therefore, we evaluated whether daily protein intake was associated with
skeletal muscle strength in older adults.
Methods: We used data from 6,503 participants aged 60 years and over from the Korean National Health and Nutrition
Examination Survey conducted in 2014 and 2017. To evaluate skeletal muscle strength, the participants’ handgrip strength (HGS)
was measured using a digital grip strength dynamometer. The participants’ dietary protein intake was assessed using a semi-quan-
titative food frequency questionnaire.
Results: HGS increased with daily protein intake, and daily protein intake was negatively associated with the prevalence of
low skeletal muscle strength, but there were no differences in daily protein intake, HGS, or low skeletal muscle strength prevalence
after adjustment for the covariates, including physical activity.
Conclusion: Further studies focusing on the interactions between the amount of dietary protein consumed and other factors
are needed to evaluate the relationship between the amount of daily protein intake and skeletal muscle strength.
Key Words: Dietary proteins, Handgrip strength, Muscle strength, Older adults, Possible sarcopenia
INTRODUCTION sarcopenia is a major medical issue.
A reduction in skeletal muscle strength is independently
An age-related decline in the mass, strength, and function related to physical disability [9] and mortality [10]. Several
of skeletal muscle is associated with an increased risk of studies have shown that skeletal muscle strength is a better
reduced physical capacity [1], poorer quality of life [2], and indicator of individuals with functional impairment and frailty
adverse health outcomes, such as metabolic disturbances [3], than skeletal muscle mass in older adults [10,11]. Therefore,
falls and fractures [4], and mortality [5] and places a high a new entity of “possible sarcopenia” defined by low skeletal
socioeconomic burden on older people [6]. The prevalence of muscle strength has been emphasized to contribute to higher
sarcopenia is 5-13% in those aged 60-70 years worldwide awareness and facilitate timely interventions for sarcopenia
[7], and in Korea, the prevalence was 4.6-14.5% in men and [12].
6.7-14.4% in women aged 70 years and over [8]; thus, Several studies have examined protein intake among various
Received January 20, 2021; revised May 13, 2021; accepted May 31, 2021.
Corresponding author: Sang-Wook Song, Department of Family Medicine, St. Vincent’s Hospital, College of Medicine, The Catholic University of Korea,
93 Jungbu-daero, Paldal-gu, Suwon 16247, Korea. E-mail: sswkoj@unitel.co.kr
Copyright Ⓒ 2021 The Korean Academ y of Clinical G eriatrics
This is an open access article distributed under the term s of the Creative Com m ons Attribution N on-Com m ercial License (http://creativecom m ons.org/licenses/by-nc/4.0) w hich
perm its unrestricted non-com m ercial use, distribution, and reproduction in any m edium , provided the original w ork is properly cited.Ha-Na Kim, Sang-Wook Song: Daily Protein Intake and Skeletal Muscle Strength 41
factors influencing the decline in skeletal muscle strength each food item was consumed during the previous year. The
[13,14], but the findings are inconsistent [15,16]. Furthermore, daily amount of protein consumed was estimated from the
no studies have investigated the association between low sum of the intake of each food item, based on the food com-
amount of daily protein intake and skeletal muscle strength in position tables of the Rural Development Administration, in
older Koreans. Therefore, we evaluated whether daily protein combination with the nutrient database of the Korea Health
intake is associated with skeletal muscle strength in Koreans Industry Development Institute [18]. Daily protein intake,
aged 60 years and over, using data from the Korean National defined as the amount of daily protein consumed per kilo-
Health and Nutrition Examination Survey (KNHANES). gram body weight, was classified into three categories: low
(＜0.8 g/kg body weight/day), moderate (0.8-1.2 g/kg/d), and
MATERIALS AND METHODS high (＞1.2 g/kg/d) protein intake [19].
1. Study population 3. Measuring handgrip strength
We used KNHANES data collected in 2014 and 2017. To evaluate skeletal muscle strength, the participants’
KNHANES is performed by the Korean Centres for Disease handgrip strength (HGS) was measured by trained examiners
Control and Prevention at 3-year intervals to assess public using a digital grip strength dynamometer (T.K.K. 5401,
health and to provide baseline data for the development, Takei Scientific Instruments, Niigata, Japan). The dyna-
establishment, and evaluation of Korean public health policies. mometer measures up to 100.0 kg of force and has an ad-
All KNHANES participants were non-institutionalised and justable grip span. Participants were asked to sit while
aged ≥1 year; they are selected using a stratified, multi- looking forward with the elbow flexed at 90°, and squeeze
stage, cluster probability sampling design to ensure that the the dynamometer continuously with full force until a value
sample is independent, homogeneous, and nationally repre- appeared on the liquid-crystal display. The HGS was measured
sentative. Data were collected using household interviews and three times alternately for each hand, starting with the dominant
anthropometric and biochemical measurements, and included hand. The maximum value of the three measurements was
a nutrition assessment. All protocols were approved by the used as the HGS. Possible sarcopenia was defined as an
Institutional Review Board of the Korean Centres for Disease HGS ＜28 kg for men and ＜18 kg for women [12].
Control and Prevention, and all participants provided informed
consent at baseline. 4. Other variables
In this cross-sectional study, we originally evaluated data Self-reported information regarding age, sex, alcohol
on 8,608 adults ≥60 years of age selected from 31,207 consumption, smoking status, household income, extent of
KNHANES participants. We excluded participants with physical activity, and history of diabetes, hypertension, dyslipi-
missing information or values for the major variables demia, cardiovascular and cerebrovascular diseases, or any
(n=2,105). Ultimately, data for 6,503 participants were analysed
(Figure 1). The study was approved by the Institutional
Review Board of the Catholic University of Korea (IRB
approval number: VC19ZESI0213).
2. Dietary protein assessment
The participants’ dietary protein intake was assessed by
trained dietitians using the 112-item semi-quantitative food
frequency questionnaire (FFQ) [17], which is used to estimate Figure 1. Study population: data from the 2014 and 2017
Korean National Health and Nutrition Examination Survey
nutrient intake from portion size and the frequency at which (KNHANES).42 Korean J Clin Geri 2021;22(1):40-46
cancer was obtained. physical activity level; BMI; daily total energy intake; history
Information on alcohol consumption included the frequency of diabetes, hypertension, dyslipidemia, cardiovascular and
of drinking days and the number of drinks consumed per cerebrovascular diseases, or any cancer; and laboratory param-
day during the year preceding the KNHANES household eters, including serum creatinine, high sensitivity C-reactive
interview. We used the Korean version of a “standard drink” protein levels, and lipid profiles including total cholesterol,
(any drink that contains 10 g pure alcohol) [20]; alcohol high-density lipoprotein cholesterol, and triglyceride levels.
consumption was classified into three categories: abstinence The associations between dietary protein intake and HGS
(no alcoholic drinks consumed within the last year), moderate were analysed using multiple logistic regression after adjusting
drinking (≤14 standard drinks consumed by men and ≤7 for covariates. All statistical analyses were performed using
by women per week), and heavy drinking (＞14 standard SAS (ver. 9.2; SAS Institute, Cary, NC, USA). A P value
drinks consumed by men and ＞7 by women per week). ＜0.05 was considered to reflect significance.
Cigarette smoking was divided into three categories based on
current use: non-smoker, ex-smoker, and current smoker. RESULTS
Household income was divided into monthly equivalent
household values (in quartiles), estimated as total income divided 1. Characteristics of the study population by
by the square root of the number of household members. possible sarcopenia
Participants were asked about their extent of physical activity This study examined data from 6,503 participants (2,935
during the week preceding the interview; this was classified as men and 3,568 women). The prevalence of possible sarcopenia
low or not. Low-level activity was defined as ≤150 min of was 8.3% and 23.5% in men and women, respectively. Those
moderate-intensity exercise or ≤75 min of vigorous exercise with possible sarcopenia tended to be older, and had higher
per week [21]. Body weight and height were measured with proportions of low-level activity, lower household income,
the participants wearing light indoor clothing without shoes. lower proportion with dyslipidemia, higher proportion with
Body weight and height were measured with the participants stroke, were less obese, and lower daily energy intake, higher
wearing light indoor clothing without shoes. Body mass index proportion of energy from carbohydrates, and lower proportions
(BMI) was calculated as weight (kilograms) divided by from protein and fat (Table 1).
height squared (meters squared). Venous blood samples were
drawn from the study participants after fasting for 12 hours 2. Handgrip strength according to daily protein
or overnight. intake
Table 2 shows the mean of HGS by daily protein intake.
In both men and women, HGS increased as daily protein intake
5. Statistical analyses increased (P for trend ＜0.001), but there were no significant
We used the SAS PROC SURVEY module, which con- differences in HGS according to daily protein intake after
siders strata, clusters, and weights, to analyse the data. All adjustment for age, smoking status, alcohol consumption,
analyses were performed using the KNHANES sample physical activity, household income, BMI, daily total energy
weightings. Sex-specific features were evaluated using in- intake, history of comorbidities, serum creatinine, high sensi-
dependent t-tests for continuous variables and chi-square test tivity C-reactive protein levels, and lipid profiles.
for dichotomous variables. Data are expressed as mean±
standard error or percentages. Differences in HGS according 3. Association between daily protein intake and
to dietary protein intake were evaluated using analysis of possible sarcopenia
covariance. The following were all used as covariates: age; Table 3 shows the unadjusted, age-adjusted, and multi-
alcohol consumption; smoking status; household income; variate-adjusted odds ratios of possible sarcopenia accordingHa-Na Kim, Sang-Wook Song: Daily Protein Intake and Skeletal Muscle Strength 43
Table 1. Characteristics of the study population by possible sarcopenia
Men Women
Possible sarcopenia Possible sarcopenia
Total Total
Yes No P value Yes No P value
N 2,935 275 2,660 - 3,568 818 2,750 -
Age, years 69.0±0.1 75.9±0.4 68.4±0.144 Korean J Clin Geri 2021;22(1):40-46
Table 2. Mean handgrip strength according to daily protein intake
†
Daily protein intake
Handgrip strength* P value P for trend P value‡ P for trend‡
Low Moderate High
Men 34.4±0.3 36.3±0.2 36.8±0.3Ha-Na Kim, Sang-Wook Song: Daily Protein Intake and Skeletal Muscle Strength 45
pensable amino acids [29], or the source of the dietary protein and SW Song analysed and interpreted the data; HN Kim
[30] might affect skeletal muscle health, but these factors wrote the manuscript; SW Song supervised writing of the paper
were not included in this study. Therefore, additional research and provided critical revisions; HN Kim and SW Song read
should consider the association between total daily protein, and approved the final manuscript.
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