Vitamin D deficiency is strongly linked to increased mortality, especially in younger and middle-aged people, and is particularly associated with diabetes-related deaths, suggests a study presented in a poster* last week at this year's Annual Meeting of the European Association for the Study of Diabetes (EASD) in Barcelona, Spain (16-20 Sept).
Researchers from the Medical University of Vienna in Austria analysed the effects of low 25-hydroxyvitamin D (25D) (referred to as vitamin D) levels in the blood on overall and cause-specific mortality in a large study cohort covering all age groups, and taken from a population with minimal vitamin D supplementation in old age.
They accessed data from the records of all 78,581 patients (mean age 51.0 years, 31.5% male) who had a vitamin D (25D) measurement taken at the Department of Laboratory Medicine, General Hospital of Vienna between 1991 and 2011, which were matched with the Austrian national register of deaths. The first three years of mortality following the vitamin D measurement were excluded from the analysis, and patients were followed for up to 20 years where possible, with a median follow-up of 10.5 years.
The commonly used cut off blood level for vitamin D deficiency is 50 nmol/L, and the researchers calculated risk and death for low and high levels of vitamin D - 10 nmol/L and 90 nmol/L respectively.
Vitamin D levels of 10 nmol/L or less were associated with a 2-3 fold increase in risk of death, with the largest effect being observed in patients aged 45 to 60 years (2.9 times increased risk). Levels of 90 nmol/L or greater were associated with a reduction in all-cause mortality of 30-40%, again with the largest effect being found in the 45 to 60-years-old age group (a 40% reduction in risk). No statistically significant associations between vitamin D levels and mortality were observed in patients over the age of 75.
With regard to cause-specific mortality, the researchers were surprised to find the strongest associations of vitamin D were with causes of death other than cardiovascular disease and cancer. Differences between the age groups were even more pronounced for these causes of death and, again, the largest effect was found in patients aged 45 to 60 years. Further subdivision of these non-cardiovascular, non-cancer causes of death revealed the largest effect was for diabetes with a 4.4 times higher risk of death from the disease in the vitamin D deficient group (less than or equal to 50 nmol/L) than for study participants whose serum vitamin D was above 50 nmol/L.
The researchers concluded: "Our survival data from a large cohort, covering all age groups, from a population with minimal vitamin D supplementation at old age, confirm a strong association of vitamin D deficiency (under 50 nmol/L) with increased mortality. This association is most pronounced in the younger and middle-aged groups and for causes of deaths other than cancer and cardiovascular disease, especially diabetes."
They added: "Our findings strengthen the rationale for widespread vitamin D supplementation to prevent premature mortality, emphasize the need for it early in life and mitigate concerns about a possible negative effect at higher levels."
*Marculescu R, Endler G, Yang L, et al. Poster 325 Vitamin D deficiency, overall and cause-specific mortality: the impact of age and diabetes. The European Association for the Study of Diabetes (EASD), Barcelona, Spain (16-20 Sept)