Vitamin D is an essential, fat soluble compound that can be made by the body in response to sunlight, and it is also acquired through the diet. When it was discovered, this vitamin was characterised by its ability to cure rickets and its effect on the health of the bones, and maintenance of bone health continues to be one of the best known roles of vitamin D today. Over the years, researchers have determined that a number of other conditions may be influenced by the body's vitamin D levels, including cardiovascular disease, cancer, hypertension, diabetes, immune system function, and neuropsychological function.
In spite of the large amount of work conducted into the relationship between vitamin D and various medical conditions, there is quite a bit of controversy and conflict between studies, and the efficacy of vitamin D in the prevention and treatment of a number of medical conditions is often debated.
A group of researchers from the United Kingdom decided to take a large scale approach to investigation of the relationship between vitamin D concentration and health, and used data from a very large population study, made up of almost 15000 middle aged and senior citizens of both sexes, to determine the effect of this vitamin on health. Vitamin D levels were measured at the beginning of the study, and health incidents and mortality rates continued to be monitored in these people for a thirteen year period.
The study came to some interesting conclusions. Firstly, in both men and women, higher blood vitamin D concentrations predicted lower chance of dying from any cause over the study period. In addition, higher vitamin D correlated to reduced occurrence of, and fewer deaths from heart disease, respiratory disease and fractures, but vitamin D levels did not have any impact on incidence of or deaths from cancer.
In drawing these conclusions, the study took a number of issues into account, including general health and nutrition status, activity, and even socioeconomic factors. This doesn't completely rule out the notion that low vitamin D is an effect of illness, but it does provide significant evidence that higher vitamin D levels lower the chances of illness and death, specifically from cardiorespiratory disease and fractures, in middle aged and elderly people.
This was a very broad study, and there is a lot of research that needs to be done to tell us how and why this is the case, but in the meantime, people who are interested in preserving their health could do a lot worse than making sure they're getting better than adequate levels of vitamin D.
Khaw KT, Luben R, Wareham N. Serum 25-hydroxyvitamin D, mortality, and incident cardiovascular disease, respiratory disease, cancers, and fractures: a 13-y prospective population study. Am J Clin Nutr. 2014 Nov;100(5):1361-70.