Doesn’t it seem like when it comes to nutrition there are more opinions than facts to go around? Every day we hear new theories about diets, and supplements, and the best foods to eat. My role is to take the mystery out of good nutrition, and look at the science. Welcome to the Nutrition Facts Podcast. I’m your host Dr. Michael Greger. And I’m here to bring you an evidence-based approach to the best way to live a healthier longer life.
Today, we ask is it necessary to take vitamin D supplements? Vitamin D, which is made mostly by animals, including ourselves, when we’re exposed to sunlight, may help us enjoy a longer life based on randomized, controlled studies. It’s also been shown to improve pain from menstrual periods and help prevent respiratory infections.
In our first story we ask how much vitamin D should we take?
In my nine-part video series on vitamin D back in 2011, I noted that the relationship between vitamin D levels and mortality appeared to be a U-shaped curve meaning low vitamin D levels were associated with increased mortality. But so were levels that were too high, with the apparent sweet spot around 75 or 80 nanomoles per liter [nmol/L], based on individual studies.
Why might higher D levels be associated with higher risk? Well, this was a population study; so, you can’t be sure which came first. Maybe the vitamin D led to higher risk. Or maybe higher risk led to the vitamin D, meaning maybe those who weren’t doing as well were prescribed vitamin D. Maybe it’s because these were Scandinavian studies, where they tend to take a lot of cod liver oil as the vitamin D supplement, one spoonful of which could exceed the tolerable upper daily limit of intake for vitamin A which could have negative consequences, even if you don’t inject it into your penis.
I was surprised to see cod liver oil listed among the long list of things men have tried to inject into themselves because they felt they were coming up short, though may have ended up even shorter after all the reconstructive surgery.
Anyways, an updated meta-analysis has shown that as population vitamin D levels go up, mortality appears to go down, and stay down which is good, because then we don’t have to test to see if we’re hitting just the right level.
Routine testing of vitamin D levels is not recommended. Why? Well, it costs money, and in most people, levels come right up to where you want them with sufficient sun, or supplementation. So, they figure what’s the point?
So, what’s a safe dose that will likely get us to the purported optimal level? 1,000 units a day should get most people up to the target 75 nmol/L (which is 30 ng/mL). But by most people, they mean 50%. To get around 85% of the population up to 75 would require 2,000 a day. 2,000 international units a day would shift the curve. That way, we can take the average person into the desired range without fear of toxicity. You can take too much vitamin D, but you don’t tend to see problems until blood levels get up around 250, which would take consistent daily doses in excess of 10,000.
Note that if you’re overweight, you may want to take 3,000, or if obese, even more than that. If you’re over age 70, and not getting enough sun, it may take 3,500 units to get that same 85% chance of bumping your levels past the target. Again, no need for the average person to test and retest, since a few thousand a day should bring almost everyone up without risking toxicity.
Okay, but then why did the Institute of Medicine set the Recommended Daily Allowance at 600 to 800 units? In fact, official recommendations are all over the map ranging from just 200 a day, all the way up to 10,000 a day.
In our next story we learn how a daily dose of 4,000 IU of vitamin D is recommended for elders at high risk for falling to improve muscle strength and balance, though there is something that works even better.
We’ve known for over 400 years that muscle weakness was a common presenting symptom of vitamin D deficiency. Bones aren’t the only organs that respond to vitamin D; muscles do too. But, as we age, our muscles lose vitamin D receptors, perhaps helping to explain the loss in muscle strength as we age.
And indeed, vitamin D status does appear to predict the decline in physical performance as we age, with lower vitamin D levels linked to poorer performance. But, maybe the low vitamin D doesn’t lead to weakness; maybe the weakness leads to low vitamin D. Vitamin D is the sunshine vitamin, and so, if you’re too weak to run around outside, that could explain the correlation with lower levels. To see if it’s cause and effect, you have to put it to the test.
There’s been about a dozen randomized controlled trials: vitamin D supplements versus sugar pills. Put all the studies together, and older men and women do get significant protection from falls with vitamin D, especially among those who start out with relatively low levels, leading the conservative USPSTF, the U.S. Preventive Services Task Force, the official prevention guideline-setting body, and the American Geriatric Society to recommend vitamin D supplementation for those at high risk for falls.
We’re not quite sure of the mechanism, though. Randomized, controlled trials have found that vitamin D boosts global muscle strength, particularly in the quads, which are important for fall prevention—though vitamin D supplements have also been shown to improve balance. So, it may also be a neurological effect, or even a cognitive effect. We’ve known for about 20 years that older men and women who stop walking when a conversation starts are at particularly high risk of falling. Over a six-month timeframe, few of those who could walk and talk at the same time would go on to fall, but 80% of those who stopped when a conversation was initiated ended up falling.
Other high risk groups that should supplement include those who’ve already fallen once, or are unsteady, or on a variety of heart, brain, and blood pressure drugs that can increase fall risk. There’s also a test called “Get-Up-and-Go,” which anyone can do at home. You time how long it takes you “to get up from an armchair, walk 10 feet, turn around, walk back, and sit down.” If it takes you longer than ten seconds, then you may be at high risk.
So, how much vitamin D should you take? It seems to take at least 700 to a thousand units a day. The American Geriatric Society recommends a total of 4,000 a day, though, based on the rationale that this should get about 90% of people up to the target vitamin D blood level of 75 nanomoles per liter. 1,000 should do it for the majority of people, 51%, but they recommend 4,000 to capture 92% of the population. Then, you don’t have to routinely test levels, since you would get most people up there, and it’s considerably below the proposed upper tolerable intake of 10,000 a day. They do not recommend periodic megadoses.
Because it’s hard to get patients to comply with pills, why not just give people one megadose, like 500,000 units, once a year, like when you come in for your flu shot, or something? So, every year, you can at least guarantee that everyone gets an annual spike in D levels that lasts a few months. It’s unnatural, but certainly convenient (for the doctor, at least). The problem is that it actually increases fall risk—a 30% increase in falls in those first three months of the spike. Similar results were found in other megadose trials. It may be a matter of “too much of a good thing.”
See, “vitamin D may improve physical performance, reduce chronic pain, and improve mood” so much that you start moving around more, and, thereby, increase fall risk. You give people a whopping dose of D, and you get a burst in physical, mental, and social functioning, and it may take time for your motor control to catch up with your improved muscle function. It would be like giving someone a sports car all of a sudden when they’ve been used to driving some beater. You gotta take it slow.
It’s possible, though, that such unnaturally high doses may actually damage the muscles. The evidence they cite in support is a meat industry study showing you can improve the tenderness of steaks by feeding steers a few million units of vitamin D. So, the concern is that such high doses may be over-tenderizing our own muscles, as well. So, yeah, higher D levels are associated with a progressive drop in fracture risk, but too much vitamin D may be harmful.
The bottom line is that vitamin D supplementation appears to help, but the strongest and most consistent evidence for prevention of serious falls is exercise. If you compare the two, yes, taking vitamin D may lower your fall risk, compared to placebo. But, strength and balance training, with or without vitamin D, may be even more powerful.
Finally, today we look at the results of 56 randomized clinical trials to see what vitamin D can do to extend our lifespan.
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 affixed to tenement buildings so babies could benefit from the sun. Are we in a similar situation now, where the medical profession has just not caught up with the science?
Researchers have documented correlations between all sorts of good things and 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.
But when 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 placebos, 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 D3, though, the type derived from plants and animals, not vitamin 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. A 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 exercise. Though no, it does not seem to reduce the adverse effects of earthquakes.
We would love it if you could share with us your stories about reinventing your health through evidence-based nutrition. Go to NutritionFacts.org/testimonials. We may be able to share it on our social media to help inspire others. To see any graphs charts, graphics, images or studies mentioned here, please go to the Nutrition Facts Podcast landing page. There you’ll find all the detailed information you need plus links to all of the sources we cite for each of these topics.
For recipes, check out my “How Not to Die Cookbook.” It’s beautifully designed, with more than 100 recipes for delicious and nutritious meals. And all the proceeds I receive from the sales of all my books goes to charity. NutritionFacts.org is a non-profit, science-based public service, where you can sign up for free daily updates on the latest in nutrition research via bite-sized videos and articles.
Everything on the website is free. There’s no ads, no corporate sponsorship. It’s strictly non-commercial. I’m not selling anything. I just put it up as a public service, as a labor of love – as a tribute to my grandmother, whose own life was saved with evidence-based nutrition. Thanks for listening to Nutrition Facts. I’m your host, Dr. Michael Greger.