Associations between plasma and dietary vitamin C, grip strength, and physical function: A cross-sectional analysis in the EPIC-Norfolk cohort

Vitamin C is important for several biological processes that are relevant to skeletal muscle. It is involved in the synthesis of collagen and carnitine, acts as an antioxidant (1) , and recent animal studies have shown that deficiency can lead to muscle atrophy and loss of strength and physical function (2,3) . Maintaining an adequate vitamin C status may be important for maintaining muscle mass, muscle strength and physical function during ageing and for preventing sarcopenia. Prior epidemiological research investigating vitamin C and muscle strength or physical function in humans has mainly focused on dietary vitamin C. In this study, we investigate associations between both plasma and dietary intakes of vitamin C and measures of muscle strength and physical function in adult men and women. Cross-sectional data from the third health check of the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk cohort were provided. Over 5,000 participants (age 48 to 92 years) had full datasets for analysis. Plasma vitamin C was measured from non-fasting blood samples by fluorometric assay and organised into categories for analysis (low <25mmol/L, suboptimal 25 to <50mmol/L, optimal ≥50mmol/L). Dietary vitamin C intake was assessed using a food frequency questionnaire and categorised into quintiles for analysis. Hand grip strength was measured using a hand-held dynamometer and normalised by dividing by height2 (HGSht). Physical function was assessed using 4m gait speed (GS) and time to complete 5 chair stands (CS). Multiple linear regression, including relevant lifestyle, medical, biological, and dietary covariates (percent energy intake (EI) from protein, and ratio of EI to estimated energy requirement), was used to investigate associations between dietary and plasma vitamin C and HGSht, GS, and CS. Least square means were calculated via linear regression analysis. Women with low versus optimal plasma vitamin C had 0.54 kg/m2 lower HGSht (p = 0.009), 0.11m/s slower GS ( p < 0.001), and an increased CS time of 1.03s ( p = 0.028). In men, no association was found between plasma vitamin C and grip strength. Men with low versus optimal plasma vitamin C had 0.05 m/s slower GS ( p = 0.01) and an increased CS time of 0.71s ( p = 0.026). No associations were found between dietary vitamin C and grip strength in men or women, or with GS and CS in men. Compared with Q1, women in Q2 and Q5 of dietary vitamin C intake had 0.04 m/s faster GS ( p < 0.01 for both), and women in Q4 and Q5 had 0.67s ( p = 0.002) and 0.57s ( p = 0.013) faster CS times respectively. These results suggest that maintaining optimal vitamin C status may be important for maintaining physical function in both men and women. These associations should be investigated prospectively to confirm our findings.