Where Vitamin D Supplements Fail

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:

And check out these other videos on vitamin D’s potential benefits:

For additional videos on supplements, see:

In health,
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:

Turmeric Curcumin Put to the Test for Inflammatory Bowel Disease

My video Striking with the Root: Turmeric Curcumin and Ulcerative Colitis tells the story how this amazing discovery was made, and how curcumin stacks up against pharmacological interventions.

Despite evidence going back 40 years that the turmeric spice component curcumin possesses significant anti-inflammatory activity, it wasn’t until 2005 that it was first tested on inflammatory bowel disease. Why did it take so long? Well, who’s going to fund such a study? Big Curry? Even without corporate backing, individual physicians from New York decided to ask the next five patients with ulcerative colitis who walked through their office doors to start curcumin supplements.

“Ulcerative colitis (UC) is a debilitating, chronic, relapsing-remitting [i.e., it comes and goes] IBD [inflammatory bowel disease] that afflicts millions of individuals throughout the world and produces symptoms that impair quality of life and ability to function.” As with most diseases, we have a bunch of drugs to treat people, but sometimes these medications can add to disease complications, most commonly nausea, vomiting, headaches, rash, fever, and inflammation of the liver, pancreas, and kidneys, as well as potentially wiping out our immune system and causing infertility. Most ulcerative colitis patients need to be on drugs every day for the rest of their lives, so we need something safe to keep the disease under control.

So how did those five patients do on the spice extract? Overall, all five subjects improved by the end of the study, and four of the five were able to decrease or eliminate their medications. They had “more formed stools, less frequent bowel movements, and less abdominal pain and cramping. One subject reported decreased muscle soreness, commonly felt after his exercise routine.” This, however, was what’s called an open-label study, meaning the patients knew they were taking something so some of the improvement may have just been the placebo effect. In 2013, another small open-label pilot study found encouraging results in a pediatric population, but what was needed was a larger scale, double-blind, placebo-controlled trial.

And, researchers obliged. They took a bunch of people with quiescent ulcerative colitis and gave them either turmeric curcumin along with their typical anti-inflammatory drugs, or a placebo and their drugs. In the placebo group, 8 out of 39 patients relapsed, meaning their disease flared back up. In the curcumin group, however, only 2 out of 43 relapsed, significantly fewer. And, relapse or not, clinically, the placebo group got worse, while the curcumin group got better. Endoscopically, which is objectively visualizing the inside of their colons, doctors saw the same thing: trends towards worse or better.

The results were stunning: a 5 percent relapse rate in the curcumin group compared with a 20 percent relapse rate in the conventional care group. It was such a dramatic difference that the researchers wondered if it was some kind of fluke. Even though patients were randomized to each group, perhaps the curcumin group just ended up being much healthier through some chance coincidence, so maybe it was some freak occurrence rather than curcumin that accounted for the results? So, the researchers extended the study for another six months but put everyone on the placebo to ensure the initial findings were not some aberration. The curcumin was stopped to see if that group would then start relapsing, too—and that’s exactly what happened. Suddenly, they became just as bad as the original placebo group.

The researchers concluded: “Curcumin seems to be a promising and safe medication for maintaining remission in patients with quiescent ulcerative colitis.” Indeed, no side effects were reported at all. So, “Curry for the cure?” asked an accompanying editorial in the journal of the Crohn’s and Colitis Foundation of America. “Can curcumin be added to our list of options with respect to maintaining remission in ulcerative colitis? What is noteworthy about this trial is the fact that not only did the authors demonstrate a statistically significant decrease in relapse at 6 months, but a statistically significant improvement in the endoscopic index as well. Equally telling is the fact that upon withdrawal of curcumin the relapse rate quickly paralleled that of patients treated initially with placebo, implying that curcumin was, in fact, exerting some important biologic effect.”

Similarly, a Cochrane review concluded in 2013 that curcumin may be a safe and effective adjunct therapy. Cochrane reviews take all the best studies meeting strict quality criteria and compile all the best science together, which is normally a gargantuan undertaking. Not so in this case, however, as there is really just that one good study.


Turmeric is one of the most popular trending topics, and I encourage you to check out the most popular turmeric videos, including:

For more on ulcerative colitis and inflammatory bowel disease, see:

In health,
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:

Is It Healthier to be Happier?

More than 60 years ago, the World Health Organization defined health as a “state of complete physical, mental, and social well-being and not merely the absence of disease or infirmity.” Just because you’re not depressed doesn’t necessarily mean you’re happy. But, if you look in the medical literature, there are 20 times more studies published on health and depression than there are on health and happiness. In recent years, though, research on positive psychology has emerged, and we’re now asking what we can do to increase our success, functioning, and happiness. Although these are all inherently good in themselves, what about the question I address in my video Are Happier People Actually Healthier?

“There is growing evidence that positive psychological well-being is associated with reduced risk of physical illness,” but it’s not surprising that healthier people are happier than sick people. “The intriguing issue is whether psychological well-being protects against future illness or inhibits the progression of chronic disease.” To figure out which came first, you’d have to get more than just a snapshot in time. You would need prospective studies, meaning studies that go forward over time, to see if people who start out happier do, in fact, live longer. A review of such studies indeed “suggests that positive psychological well-being has a favorable effect on survival in both healthy and diseased populations.”

Not so fast.

Yes, positive states may be associated with less stress, less inflammation, and more resilience to infection. But, positive well-being may also be accompanied by a healthy lifestyle that itself reduces the risk of disease. Happy people tend to smoke less, exercise more, drink less alcohol, and sleep better. So, maybe happiness leads to health only indirectly. The apparent protective effect of positive psychological well-being, however, persists even after controlling for all these healthy behaviors. This means that even at the same level of smoking, drinking, exercising, and sleeping, happier people still seem to live longer.

Ideally, to establish cause-and-effect definitively, we’d do an interventional trial, in which participants would be assigned at random to different mood levels and tracked for health outcomes. It’s rarely feasible or ethical to randomly make some people’s lives miserable to see what happens, but if you pay people enough you can do experiments like the one whose objective stated: “It has been hypothesized that people who typically report experiencing negative emotions are at greater risk for disease and those who typically report positive emotions are at less risk.” Researchers tested this using the common cold virus. Three hundred and thirty-four healthy volunteers were assessed for how happy, pleased, and relaxed they were, or how anxious, hostile, and depressed. Subsequently, they were given nasal drops containing cold rhinoviruses to see who would be more likely to come down with the cold. Who would let someone drip viruses into their nose? Someone paid $800, that’s who!

Now, just because you get exposed to a virus doesn’t mean you automatically get sick. We have an immune system that can fight it off, even if the virus is dripped right into our nose. But, whose immune system fights better?

In one-third of the bummed out folks, their immune systems failed to fight off the virus and they came down with a cold. But only about one in five got a cold in the happy group. Could it be that those with positive emotions slept better, got more exercise, or had lower stress? No. It appears that even after controlling for the healthy practices and levels of stress hormones, happier people still appear to have healthier immune systems and a greater resistance to developing the common cold.

It also works with the flu. When researchers repeated the study with the flu virus, increased positive emotions were associated with decreased verified illness rates, just like in their earlier study on colds. These results indicate that feeling vigorous, calm, and happy may play a more important role in health than previously thought.


Okay, so if happiness improves health, how do we improve happiness? That’s the subject of my video Which Foods Increase Happiness?.

I’m as guilty as the rest of my colleagues for focusing on mental illness rather than mental health (though my Laughter as Medicine video is a rare exception). It’s a consequence of what’s out there in the medical literature, though I’ll make a special effort to highlight new studies in this area as they’re published. I do, however, have a number of videos on preventing and treating negative mood states, such as depression and anxiety:

What about psychiatric medications? See my videos Do Antidepressant Drugs Really Work?, Exercise vs. Drugs for Depression, and Saffron vs. Prozac.

Interested in other ways to improve our immune system? Check out Using the Produce Aisle to Boost Immunity.

In health,
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: