Taking ordinary doses of vitamin D may improve survival, according to a report that analyzed results from 18 independent studies of vitamin D supplementation. The study looked at data involving 57,000 people from developed countries in climates with pronounced seasonal variation in sunlight, including the U.S., New Zealand and several countries in Europe. The body requires sunlight to make vitamin D, and in the absence of sun the vitamin must come from food or supplement sources. The report was published in the September 10th edition of Archives of Internal Medicine.
Death from chronic diseases such as cancer, diabetes and cardiovascular disease may be linked to the part of the earth a person inhabits, with people who live further from the equator being more likely to die of a chronic disease. This could be because less available sunlight during the winter months in colder regions results in lower vitamin D levels. To investigate if differences in vitamin D levels might account for differences in chronic disease prevalence, researchers decided to compare the death rates in people with and without supplemental vitamin D3 (cholecalciferol) or vitamin D2 (ergocalciferol).
The overall analysis compared groups taking a vitamin D supplement with those not taking a supplement and found that an average daily dose of 528 International Units (the standard unit for vitamins) was associated with a 7% reduction in the chances of dying within the next 6 years.
In all 18 individual trials, taking vitamin D pills increased blood levels of the active form of the vitamin up to 5 times the level seen in patients not taking the supplement. The study did not examine the effects of different doses, or if the effects varied by what each person's vitamin D level was at the beginning of the study. In addition, the study did not look at death from cardiovascular disease separately, simply at all causes of death combined over the period of the study, so the vitamin's exact effect on heart disease death in particular is not clear.
The researchers aren't sure exactly how vitamin D decreases risk of death, but since scientists know that it acts as a hormone affecting the skeletal, digestive, immune and vascular systems, they theorize that vitamin D might help inhibit tumor growth and interfere with the deposit of fatty substances in the arteries. More research is needed to confirm the findings and determine the best doses for protection against disease. If you take vitamin D it is suggested that you stick to the recommended dose of 400 IU per day, or the dose your doctor recommends. Vitamin D should not be taken to try to prevent or cure any disease, but as part of an overall healthy lifestyle.