Recently I have heard of a few mainstream news articles about studies that "prove" vitamin D is useless at preventing and treating disease, one of them being a JAMA "review" stating that vitamin D is ineffective in treating hypertension. Fortunately, Life Extension has already written a rebuttal, which saves me a lot of time in coming up with one myself.
Of the 46 studies used in the review, only 16 included participants that gave an average systolic blood pressure of over 140mmHg, so most of the 4,541 participants did not even have hypertension. If it proved anything, it is that vitamin D does not lower blood pressure in those within healthy ranges. One of the studies on normotensive participants actually used doses often considered too low to be therapeutic (200, 400 or 600 IU), while another excluded people with clinical vitamin D deficiency, and yet another excluded people with hypertension but was still included to prove a lack of effect on hypertension! Another tested the effect of one oral dose of 100,000 IU on patients with peripheral arterial disease, hoping for positive changes after just one month. PAD doesn't appear overnight, so why would it instantly disappear? And besides, often you simply do not absorb too much more of a vitamin than what you need, but 100,000 IU is probably overdosing anyway so I wouldn't even recommending injecting that amount. Another failed study showed no effect of 50,000 IU per week for six months in patients with heart failure. If you wanted an effect, you should probably have started earlier instead of telling people that fat is unhealthy, the sun is evil and supplementation is a waste of time.
However, some of the studies used in this review actually reported a positive effect of vitamin D on hypertension. In one of these, 34 type II diabetic patients with serum vitamin D under 20ng/mL were given 100,000 IU of vitamin D2 or placebo, and monitored for eight weeks. The vitamin D2 decreased systolic blood pressure by 14mmHg, and this was deemed "significant". In another, 148 women with serum vitamin D under 20ng/mL were prescribed 1,200mg of calcium with or without 800IU of vitamin D3 for eight weeks. 81% of the women taking vitamin D showed a decrease in systolic blood pressure of 5mmHg or more, compared with 47% in the calcium-only group. Then, in a double-blind study of 283 African-Americans using doses as high as 4,000IU per day, blood pressure was once again significantly lowered. But is vitamin D really useless for heart failure? Another on 23 patients with chronic heart failure involved 13 of the patients being given 4,000 IU daily over six months, and resulted in a lower systolic blood pressure and higher ejection fraction among the treated patients.
As for mortality rates, vitamin D may also have a benefit there. A year-long study of 510 patients with serious, life-threatening illnesses compared "quintiles" of vitamin D levels with mortality rates (most likely yearly), and found that while the probability of survival in the lowest quintile was 66.7%, those in the highest quintile had a 96.1% chance of survival! (Clin Chem) No one with vitamin D levels of over 58.5ng/mL died during the follow-up. A much larger study, this time with 10,170 people, investigated risk ratios for mortality for each 10-unit increase in serum vitamin D (Am J Med). The most significant decreases in mortality risk were from 0 to 10ng/mL and 10 to 20ng/mL, with smaller improvements up to 60ng/mL. So if vitamin D levels mattered more, life expectancy would probably increase, but it is hard to tell by how much because it isn't really known how many people are vitamin D deficient because of how undervalued this vitamin is. It is not tested like serum iron or even B12 are, but should be.