This inverse relationship between 25(OH) vitamin D levels and hypertension has been recently confirmed in a meta-analysis of 18 studies [91]. These various sets of data raise the question of whether vitamin D supplementation can prevent hypertension and cardiovascular events. The evidence of benefit of vitamin D supplementation from randomised trials is, however, scarce. In a small trial, 8 weeks of supplementation with vitamin D3 (800 UI/day) and calcium was reportedly more effective in reducing

systolic blood pressure than calcium alone [92]. In the Women’s selleck chemicals llc Health Initiative trial, including 36,282 postmenopausal women, vitamin D3 plus calcium supplementation did not reduce blood pressure, nor the risk of developing hypertension over 7 years of follow-up; MLN2238 nmr however, in this trial, supplementation consisted only of 400 IU/day and adherence to supplementation

was only around 60% [93]. A recent meta-analysis of eight randomised clinical trials in patients with a mean baseline blood pressure above 140/90 mmHg concluded that vitamin D reduces blood pressure modestly but significantly [94]. In summary, results from different studies are conflicting and trials specifically assessing effects of vitamin D on cardiovascular diseases as a primary endpoint are lacking. It is therefore premature to recommend supplemental vitamin D intake for the prevention of cardiovascular diseases or hypertension [95]. Vitamin D and the immune system Vitamin D receptors are present in almost all immune cells, including activated T and B lymphocytes and antigen-presenting

cells. Immune cells also express vitamin D-activating enzymes, allowing local conversion of inactive vitamin D into calcitriol within the immune system [96]. Several others autoimmune diseases such as type 1 diabetes mellitus or multiple sclerosis are more frequent in countries with less sunshine, and vitamin D deficiency in early life increases the risk of autoimmune diseases and infections later on [96, 97]. There are several epidemiological studies that have reported an association between vitamin D deficiency and susceptibility to respiratory infections, especially tuberculosis and Gram-negative infections [98]. Studies using animal models of autoimmune diseases have identified vitamin D as a potential modulator of differentiation, proliferation and secretion processes in autoimmune reaction [96]. Supplementation in humans might thus be preventive in a number of autoimmune disorders. A Finnish birth-cohort study, including >10,000 children born in 1966, showed that vitamin D supplementation during the first year of life (2,000 IU/day) was associated with a risk reduction of 78% for developing type 1 diabetes (followed up until end 1997) compared to no supplementation or use of lower doses [99]. A meta-analysis of data from four case–control studies and one cohort study support the beneficial effects of vitamin D in prevention of type 1 diabetes [100].