Dietary predictors of bone mineral density, hip fractures, mobility and muscle strength - in community-dwelling older persons

Background: The aging process involves decline of both muscle and bone mass. The loss of muscle mass is associated with decreased muscle strength and mobility, while loss of bone mass leads to osteoporosis and increased risk of fractures. This process maybe accelerated due to poor dietary quality, low energy intake and undernutrition. Fish is a good source of nutrients that are associated with preserving both muscle and bone mass. In particular, fish is contributing substantially to vitamin D intake. Overall aim: The overall aim of this PhD-project was to investigate dietary predictors of bone mineral density, risk of hip fractures, muscle strength and mobility in community-dwelling older persons. Specific aims: The aim was to summarize the available literature in a systematic literature search on randomized clinical trials investigating the effects of vitamin D supplementation (with or without calcium supplementation) on muscle strength and mobility in community-dwelling older persons, presented as a narrative systematic review and a formal meta-analysis on measures of muscle strength and mobility. The aim was to examine the association of fish intake with bone mineral density and risk of hip fractures in the Hordaland Health Study (HUSK), by conducting a) a cross sectional analysis of the association between fish intake and bone mineral density in middle - aged and older participants, and b) a prospective analysis of the association of baseline fish intake with the risk of hip fractures in the older cohort during a follow -up of ten years. The aim was to conduct a clinical observational study on weight change and mobility in community-dwelling hip fracture patients during the first two to three months after the fracture. Results: The systematic review included 15 studies. In the majority of studies, no improvements in muscle strength or mobility were observed after administration of vitamin D with or without calcium supplementation. The quantitative meta-analysis did not reveal any clinically relevant effects of vitamin D supplementation neither on handgrip strength (seven studies) nor on the timed-up-and-go test (five studies). a) Cross-sectional analyses from the HUSK study showed an association between high fish intake and higher bone mineral density in older women, but not in middleaged women or in men. b) A low intake of fish was associated with increased risk of hip fracture in older men during a follow-up of ten years. This association was not evident in older women. Among community-dwelling hip fracture patients with normal cognitive function, age and weight loss were associated with insufficient mobility two months after the fracture. Conclusions: Vitamin D supplementation had no clinically relevant effect on measures of muscle strength and mobility. Fish intake did not have consistent effects on bone mineral density and risk of hip fractures. The findings of positive effects of fish intake in subgroups but not in the entire population have to be interpreted with care. Age and weight loss were the main determinants of mobility in patients after a hip fracture. In conclusion, maintenance of weight, muscle mass and bone mineral density are key issues for health of older persons. The results of the present investigations suggest that the there is a need for more studies regarding diet and health outcomes in community-dwelling older persons