Abstract and Introduction
Abstract
Objective: Older people are more prone to vitamin D deficiency than younger populations. Individual lifestyle factors have been associated with vitamin D status. We examined the influence of a combination of lifestyle factors on vitamin D status in older men.
Participants and Measurements: In a population-based cohort study of older men (age ≥65 years), a lifestyle score was calculated from eight prudent health-related behaviours (smoking, exercise, alcohol, fish and meat consumption, adding salt, milk choices and obesity) collected via questionnaire at baseline. Blood samples were collected 5 years afterwards to measure plasma 25-hydroxyvitamin D (25OHD) levels. Associations between lifestyles and the likelihood of having plasma 25OHD levels of ≥75 versus <75 nmol/L and ≥50 versus <50 nmol/L were tested using logistic regression models.
Results: Of the 2717 men analysed, mean plasma 25OHD was 69.0 ± 23.5 nmol/L, with 20.7% having plasma 25OHD <50 nmol/L. Men engaging in ≥4 healthy lifestyle behaviours had 20% higher odds of plasma 25OHD ≥75 nmol/L (adjusted OR = 1.20, 95% CI: 1.01–1.45) compared to those with <4 healthy behaviours. No association was found for 25OHD ≥50 nmol/L. Higher physical activity was the only individual component significantly associated with vitamin D sufficiency (highest vs. lowest quintiles of physical activity, adjusted OR = 2.01, 95% CI: 1.47–2.74 for 25OHD ≥50 nmol/L, adjusted OR = 2.35, 95% CI: 1.81–3.06 for 25OHD ≥75 nmol/L).
Conclusion: Multiple healthy lifestyle behaviours are associated with better vitamin D status in older men. Further work is needed to determine the effects of promoting healthy lifestyle behaviours, including physical activity, on vitamin D sufficiency.
Introduction
Bioactive vitamin D is a hormone that stimulates the gut absorption of calcium and phosphate and is essential for bone and muscle health.[1] There are two major forms of vitamin D. Vitamin D3 is mainly synthesized in the skin after the exposure to sunlight, whereby 7-dehydrocholesterol in the skin is converted to pre-vitamin D3 during ultraviolet B radiation and is then immediately converted to vitamin D3.[1] Latitude, season, skin pigmentation, use of sunscreen and clothing cover, and outdoor activities that affect sunlight exposure can influence dermal synthesis of vitamin D3.[1] Small amounts of vitamin D are found in food such as oily fish, meat, eggs, mushrooms (a source of the other form, vitamin D2) and vitamin D fortified food.[2] The blood concentration of the intermediate metabolite, 25-hydroxyvitamin D (25OHD), is used to determine vitamin D status. Severe deficiency of vitamin D, characterized by 25OHD levels below 25 nmol/L, can have detrimental effects on health, including impaired bone mineralization.[3]
Endogenous synthesis of vitamin D declines with aging partly due to a reduction in skin 7-dehydrocholesterol, with effects on calcium absorption further exacerbated by reduced renal production of the bioactive form, 1,25-dihydroxyvitamin D (1,25(OH)2D).[4] Furthermore, decreased endogenous synthesis of vitamin D is accentuated in older people with sedentary behaviours and limited sunlight exposure, particularly those who are institutionalized, or house bound.[1] The decrease in vitamin D production and calcium absorption together lead to increased risk of negative calcium balance and bone loss in older-aged populations.[5] In recent years, vitamin D deficiency and insufficiency has been recognized as an important public health issue worldwide.[3] Australia is known for its abundance of sunshine, with most of the population obtaining vitamin D through cutaneous synthesis during sun exposure. However, the national survey indicated a lower prevalence of vitamin D deficiency (25OHD <50 nmol/L) in older age groups compared to younger groups.[6] This difference can be partially attributed to the higher likelihood of older individuals taking vitamin D supplements.[6] However, a significant number of falls- and hip fracture-related hospitalizations in the elderly Australian population remain attributable to vitamin D deficiency.[7]
In Australia, serum 25OHD level ≥50 nmol/L by the end of winter is considered adequate,[8] consistent with recommendations from the Institute of Medicine in United States of America.[9] In contrast, the UK Scientific Advisory Committee on Nutrition recommends a lower limit of vitamin D adequacy, described as a 'population protective' concentration with a serum 25OHD ≥25 nmol/L that should be achieved by 97.5% of the population throughout the year.[10] Other health institutes and organizations advocate a higher threshold of 75 nmol/L for the general population.[11] However, there is limited evidence to support higher vitamin D targets.[8,12] The European Society for Clinical and Economic Aspects of Osteoporosis and Osteoarthritis suggested the oldest old (aged >80 years) and frail older people with increased falls and fractures risk should have serum 25OHD levels of at least 75 nmol/L.[13]
Healthy lifestyle behaviours, such as regular exercise, and oily fish consumption, are beneficial for bone and muscle health; and these lifestyle factors have been associated with increased blood levels of 25OHD.[1] However, these factors have been studied individually rather than as part of a multi-lifestyle behavioural pattern. Thus, the aim of this study was to investigate the association between healthy lifestyles (a combination of behaviours) and circulating 25OHD levels in a large population of older, community-dwelling men.
Clin Endocrinol. 2023;99(2):165-173. © 2023 Blackwell Publishing
