I received a concerned email this week from a patient who had read the opinions of two internet “experts” claiming that vitamin D supplementation doesn’t protect against fractures after all, and may even be harmful. I often prescribe vitamin D3 as part of osteoporosis treatment and cancer prevention plans, so naturally I was curious as to these “experts’” objections.
Here’s one of the studies that one of these “experts” used to back up his claim. When I read this study, my jaw dropped.
If you take a vitamin D supplement, the dose you take is likely between 800 – 2000 IU (international units) per day. Occasionally I will prescribe a daily dose as high as 8000 IU for a few weeks to raise a particularly low vitamin D level, then reduce the dose for maintenance purposes. I have never had a patient experience an adverse response to doses in this range.
Perhaps now you’ll understand my surprise when I read that the study referred to above administered 500,000 IU doses of vitamin D to over 9,000 elderly adults, and my lack of surprise that falls and fractures increased very significantly as a result.
(To be clear, the 500,000 IU was not a daily dose; it was administered to each research participant as one dose, once a year.)
If your body takes in too much vitamin D, calcium is rapidly drawn from your bones into your bloodstream. Your body monitors its blood calcium levels very carefully. If blood calcium rises too high (hypercalcemia), your body produces very noticeable symptoms to let you know something is wrong. These symptoms include nausea, vomiting, weakness, excessive thirst and confusion.
Vitamin D’s potential withdrawal of bone calcium is moderated in the presence of vitamin K. Vitamin K is available in dark, leafy greens, and is also manufactured by healthy gut bacteria. Since it’s hard to be certain that a patient is eating enough leafy greens and that her gut bacteria are effective in producing vitamin K, I typically recommend combination D/K supplements for further “insurance” against excess withdrawal of bone calcium.
The extreme doses of vitamin D in the abovementioned study were given without the modulating influence of vitamin K. While we don’t know for sure, it’s a very shaky assumption that these elderly study participants were consistently eating leafy greens, or that their gut bacteria were consistently manufacturing vitamin K (the many medications taken by elders would alone bring the health of their gut bacteria into question). The authors of this study didn’t address these factors.
As such, it’s almost certain that vitamin D doses of half a million IU would have put the elderly participants into a temporary state of hypercalcemia. In that weakened and possibly confused state, is it any wonder that they fell more often? Is it really a surprise that upon falling, their calcium-depleted bones fractured more often?
We can certainly learn from this study (and others like it; unfortunately there are many) that when it comes to vitamin D supplementation, more isn’t better. In fact, more can be downright dangerous. My heart goes out to the study participants who may have suffered after being exposed to this risk.
But does this study support a sweeping conclusion that vitamin D supplementation at reasonable doses isn’t safe? Not at all.
Copyright 2015 Shani Fox, ND, LLC.