The association of dietary protein and vitamin D with body composition and exercise outcomes in cognitively normal older adults

Abstract

Background: Aging is associated with many degenerative diseases such as osteoporosis and sarcopenia due to bone and muscle loss. Sarcopenia is a prevalent geriatric syndrome, characterized by decreased skeletal muscle mass, strength and physical performance, increasing the risk of falls and fractures. Dietary factors such as protein and vitamin D appear to play a protective role, but the data are not clear. The purpose of the study was to examine the association of dietary protein and vitamin D with body composition in older adults as well as to identify if the outcomes of an exercise intervention (i.e. VO2 max, muscle mass quantity, performance and function) are influenced by these nutrients. Furthermore, we assessed the validity of different dietary intake methods (24-hour recall, 7-day food record, and the National Cancer Institute’s Dietary History Questionnaire (DHQ)-II) in older adults to ensure that the tools are measuring what people are really eating. Methods: Two studies were conducted to answer our research questions. First, we performed a tertiary analysis of data collected as part of randomized-controlled 52-week exercise trial in older adults. Dietary protein and vitamin D intakes were collected from 121 healthy older adults aged 65 years and above using a food frequency questionnaire (DHQII). Serum vitamin D was assessed by the enzyme-linked immunosorbent assay (ELISA), Immunodiagnostic Systems Ltd. Serum vitamin D, body composition and maximal oxygen consumption (VO2 max) were measured at baseline and at 52 weeks. VO2 max was measured during a graded treadmill exercise test. Muscle quantity was assessed by measuring appendicular lean muscle mass (ASM) from dual-energy X-ray absorptiometry (DXA). Muscle strength was assessed by a grip dynamometer, and performance was assessed by the senior fitness test (SFT). Second, to assess the validity of different dietary intake methods, we used data from an observational trial that examined the association between dairy intake and brain glutathione concentrations. Dietary intake was collected from 60 cognitively normal, healthy older adults aged between 60-85 years using three 24-hour recalls (3-24HR), a 7-day food record (7D), and a food frequency questionnaires (DHQII). Statistical analyses were performed using SPSS (v25, IBM) with significance of p≤0.05. Results: From the first study, mean daily protein intake was 0.87±0.36g/kg/d, 35.3% of the sample had a protein intake less than the Estimated Average Requirement (EAR) for protein (<0.66g/kg/d) and 52.6% had a protein intake less than the Recommended Dietary Allowance (RDA) of 0.8g/kg/d. Mean vitamin D intake was 465.66±264.83 IU/d, 73.5% had a daily vitamin D intake below the RDA (<600 IU), and 41.0% had an intake below the EAR (<400 IU). Mean baseline 25(OH)D level was 32.37±16.70 ng/mL (80.9±41.0 nmol/L). Baseline protein and vitamin D intake and serum 25(OH)D concentrations were not associated with body composition or any of the fitness measures. Baseline protein intake was positively associated with the change in VO2 max after 52 weeks. Baseline vitamin D intake was positively associated with the change in VO2 max, and negatively associated with the change in grip strength and change in performance after 52 weeks. Higher vitamin D intake was associated with higher ASM in the treatment group and lower ASM in the control group after 52 weeks. The change in serum 25(OH)D concentration was negatively associated with the change in grip strength after 52 weeks. From the second study, there was a significant correlation among the three dietary intake methods for energy and macronutrients, except for fat grams between DHQII and 3-24HR (r2=0.24; p=0.06). All micronutrient intakes were correlated between 3-24HR and 7D (r2 range:0.30-0.85), 20 micronutrients were correlated between DHQII and 7D (r2 range:0.11-0.85), and 17 micronutrients were correlated between DHQII and 3-24HR (r2 range:0.01-0.75). Conclusion: Our sample of older adults had a low dietary protein and vitamin D intake, which was related to their body composition and cardiac output and may potentially increase their risk of functional decline. All three methods for dietary intake assessment are adequate for use in cognitively normal older adults. Twenty-four-hour recalls may provide sufficient dietary intake information with less participant burden.