 In 1822, a Polish physician was the first to publish that sunlight could cure the vitamin D deficiency disease, rickets. His work was ignored by mainstream medicine for a century, not coming into widespread use until the 20th century, when wire cages were fixed to tenement buildings so babies could benefit from the sun. Are we in a similar situation now where the medical profession is just not caught up with the science? These have documented correlations between all sorts of good things to higher vitamin D levels, even to the point of seeing whether vitamin D supplementation might reduce the adverse effects of earthquakes. Seems to help with everything else, so why not? It's actually not as silly as it sounds. Traumatic events like natural disasters can have a significant psychological impact, which may be affected by vitamin D status. Bone researchers put supplements to the test. The purported links often didn't pan out. This lack of effect may exist in part because low vitamin D levels may just be a marker for things like aging, obesity, smoking, and inactivity. Or maybe low vitamin D didn't lead to disease, but maybe disease led to low vitamin D. Inflammation can drop D levels within the body. So just because low D levels and disease seem to be correlated doesn't mean that vitamin D deficiency is the cause. While the majority of observational studies may show a link where you just measure vitamin D levels and disease rates, in only a handful of conditions have interventional studies proven vitamin D to be effective, where you give people D supplements or placebo's and see what happens. But one of those conditions for which vitamin D supplements appear to genuinely work is helping to prevent mortality. 56 randomized clinical trials involving nearly 100,000 people between the ages of 18 and 107, mostly women, randomized to four years of vitamin D supplements or sugar pills, put all the studies together, and those given vitamin D supplements lived longer. Also specifically lowering the risk of dying from cancer. Note this effect appeared limited to vitamin D. Three, though, the type derived from plants and animals, not D2, the type derived from yeast and mushrooms. How large an effect was it? It would take 150 people taking vitamin D supplements for five years to save one life. And so if we were talking about a drug, you'd have to weigh that against the cost and side effects of dosing so many people. But when we're talking about something as safe and cheap as vitamin D supplements, it seems like a bargain to me. Similar analysis pegged the benefit at 11% in terms of reduction of total mortality, which is pretty substantial, potentially offering a life-extension benefit on par with exersons. Though no, it does not seem to reduce the adverse effects of earthquakes. The only concern that was raised is that it may give people license to like order an extra donut or something. We still have to eat healthy, right? Any longevity benefit from vitamin D would just be a small adjunct to a healthy lifestyle. But for those of us who want all the help they can get, the question then becomes, okay, how much should we take? The question I'll address next.