As I discuss in my video Do Vitamin Supplements Help with Diabetes, Weight Loss, and Blood Pressure?, review articles continue to be published touting vitamin D as a veritable cure-all. The vitamin D receptor is found in most tissues in the body, including the brain, and upwards of 2,000 genes may be regulated by vitamin D. Within 24 hours of vitamin D exposure, we can change the expression of hundreds of genes.
The term vitamin is a misnomer, though, because vitamins by definition cannot be synthesized within our body, but we can make all the D we need with sufficient sun exposure. So, rather than a vitamin, D is actually a hormone that’s produced by our skin in response to sunlight exposure. D is not just a hormone of calcium regulation and bone health; it’s also a hormone of fertility, immunity, and brain function. But is it a panacea or a false prophet?
Remember when vitamin E was the vitamin du jour, touted as a “curative for many clinical disorders”? Supplement sales of vitamin E, the “radical protector,” created a billion-dollar business that capitalized on the public’s fears. After all, those with low levels of vitamin E in their blood had a 50 percent higher cancer risk. Similar attention was directed towards vitamin A or beta-carotene. People who eat lots of greens, sweet potatoes, and other beta-carotene-rich foods have lower risk of cancer, so maybe we should give people beta-carotene pills? When they were put to the test, however, beta-carotene pills actually increased cancer rates. In fact, beta-carotene, vitamin A, and vitamin E supplements all may increase mortality, so when we buy these supplements, we’re potentially paying to shorten our lifespans. As such, I imagine you can understand the skepticism in the medical community regarding claims about vitamin D, which is now enjoying its moment in the sun.
Having a half-billion-dollar vitamin D supplement industry doesn’t help matters in terms of getting at the truth. And there’s also a highly lucrative vitamin D testing industry that loves to talk about the studies suggesting that having higher vitamin D levels may reduce the risk of heart disease, cancer, diabetes, autoimmune diseases, and infections. Most of this research, however, stems from observational studies, meaning studies that correlate higher D levels in the blood with lower disease risk, but that doesn’t mean vitamin D is the cause. It’s like the early beta-carotene data: Higher levels in the blood may have just been a marker of healthy eating. Who has high beta-carotene levels? Those who eat lots of greens and sweet potatoes. Similarly, higher levels of vitamin D may just be a marker of healthy behaviors. Who has high vitamin D levels? Those who run around outside, and those who run around outside, run around outside. Indeed, higher vitamin D levels may just be a sign of higher physical activity.
So, for instance, when you see studies showing significantly lower diabetes rates among those with higher vitamin D levels, it doesn’t mean giving people vitamin D will necessarily help. You have to put it to the test. And, when you do, vitamin D supplements fall flat on their face, showing no benefit for preventing or treating type 2 diabetes.
So, when supplement companies wave around studies suggesting vitamin D deficiency plays a role in obesity, because most population studies show that obese individuals have lower vitamin D levels in their blood, is that simply because they’re exercising less or because it’s a fat-soluble vitamin so it’s just lodged in all that fat? We might expect obese sunbathers to make more vitamin D, since they have more skin surface area, but the same exposure level for them leads to less than half the D bioavailability, because it gets socked away in the fat. This is why obese people may require a dose of vitamin D that’s two to three times higher than normal weight individuals, although they may get it back if they lose weight and release it back into their circulation. This would explain the population data. Indeed, when you put vitamin D to the test as a treatment for obesity, it doesn’t work at all.
It’s a similar story with artery health. Those with low vitamin D levels have worse coronary blood flow, more atherosclerosis, and worse artery function, but if you actually put it to the test in randomized controlled trials, the results are disappointing. Vitamin D is also ineffective in bringing down blood pressures.
This all adds to the growing body of science “casting doubt on the ability of vitamin D supplementation to influence health outcomes beyond falls, fractures, and possibly respiratory tract infection and all-cause mortality.” Wait. What? Vitamin D supplements may make you live longer? That’s kind of important, don’t you think? I talk about that in my video Will You Live Longer If You Take Vitamin D Supplements?.
Explore the other videos in my series on vitamin D, including:
- How Much Vitamin D Should You Take?
- The Optimal Dose of Vitamin D Based on Natural Levels
- The Best Way to Get Vitamin D: Sun, Supplements, or Salons?
- The Risks and Benefits of Sensible Sun Exposure
And check out these other videos on vitamin D’s potential benefits:
For additional videos on supplements, see:
- Dietary Supplement Snake Oil
- Some Dietary Supplements May Be More Than a Waste of Money
- Risk Associated with Iron Supplements
- Treating Asthma with Plants vs. Supplements?
- Broccoli: Sprouts vs. Supplements
- Antioxidants and Depression
- Are Calcium Supplements Safe?
- Are Calcium Supplements Effective?
- Industry Response to Plants Not Pills
- Resveratrol Impairs Exercise Benefits
- Lycopene Supplements vs. Prostate Cancer
- Dangers of Dietary Supplement Deregulation
- Do Vitamin C Supplements Prevent Colds But Cause Kidney Stones?
- Black Raspberry Supplements Put to the Test
Michael Greger, M.D.
PS: If you haven’t yet, you can subscribe to my free videos here and watch my live, year-in-review presentations:
- 2012: Uprooting the Leading Causes of Death
- 2013: More Than an Apple a Day
- 2014: From Table to Able: Combating Disabling Diseases with Food
- 2015: Food as Medicine: Preventing and Treating the Most Dreaded Diseases with Diet
- 2016: How Not To Die: The Role of Diet in Preventing, Arresting, and Reversing Our Top 15 Killers