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:

What Are the Best and Worst Foods?

I’ve always pictured my role primarily as providing the latest science, but you can’t understand all the new discoveries without a good foundation. The Dietary Guidelines for Americans has a chapter on food components to reduce. But, when they say things like “reduce intake of solid fats (major sources of saturated and trans fatty acids),” what does that mean in terms of which foods to cut down on?

Similarly, there’s a chapter on nutrients we should increase our intake of, so-called “shortfall nutrients.” But, when they say we need more magnesium, for example, what does that mean in terms of actual food? There’s no magnesium aisle in the grocery store. In my video What Are the Healthiest Foods? I analyze 20 different types of foods to see, based on the federal guideline criteria, which are the healthiest and which are the least healthy. There are a lot of fascinating charts in the video, so I encourage you to check it out.

To give a better idea of which foods to eat and which ones to avoid, in the video I use traffic-light labeling, so imagine that a green light means to “go ahead and eat,” yellow or amber means “caution,” and red tells you to “stop and think before you put that in your mouth.” Note these don’t correspond to the more comprehensive Traffic Light designations I detail in my book How Not to Die. When considering what foods in our diet may contribute most of the added sugars we consume, as one would suspect, sweets and sodas are red-light foods, but there are often surprising levels of extra sugar even in savory snack foods, like Ritz crackers. So, what are the top five offenders? Soda contributes 36.6% of the added sugars we consume, with grain-based desserts like donuts contributing 11.7%, Kool-Aid-type beverages contributing 11.5%, dairy desserts including ice cream contributing 6.4%, and candy contributing 6.2%.

What about caloric density? Surveying which foods contain the most calories per serving, oils join desserts and processed snack foods as the worst, though eggs, meat (including fish and poultry), nuts, seeds, and soda can’t be considered low-calorie. The top five sources of calories in the American diet are basically desserts, which contribute 6.4% of our total calories, bread, which contributes 6.0%, chicken, which contributes 5.6%, soda and other sweetened beverages, which contribute 5.3%, and pizza, which contributes 4.5%.

Which foods contain the most cholesterol? Eggs, fish, chicken, and red meat all earn the red light, while desserts, dairy, and other meats earn the yellow. Which foods contribute the highest percentages of cholesterol intake to the American diet? Number one by far is eggs (24.6%), with chicken coming in second (12.5%), beef third (11.0%), cheese fourth (4.2%), and pork fifth (3.9%).

As for saturated fat, desserts, dairy, and snack foods are all designated as red light, with eggs, chicken, fish, and red meat getting the yellow light. Most of the saturated fat in the American diet comes from cheese (8.5%), pizza (5.9%), grain-based desserts (5.8%), dairy desserts (5.6%), and chicken (5.5%).  

Salt levels are highest in lunch meat and snack foods, which both get a red light. But, Americans get most of their sodium from bread (7.3%), chicken (6.8%), pizza (6.3%), pasta (5.1%), and lunch meat (4.5%).

Trans fats are present in many foods—naturally or artificially added or created. Snack foods earn red-light levels, while oils, animal products, and animal-derived products get yellow lights. The primary contributors of trans fat in the American diet are cakes, cookies, crackers, pies, doughnuts, and other grain-based processed foods (40%), followed by animal products (21%), margarine (17%), French fries (8%), and chips and microwave popcorn (5%).

Now, to the nutrients. If you fast-forward to the 3:00 minute mark of my What Are the Healthiest Foods? video, you can see which foods are the best sources of such nutrients as calcium, fiber, magnesium, potassium, and vitamins A, C, D, E, and K. Foods in the chart with a green designation are a high source of a particular nutrient, while pale green designees are a medium source and white entries are a poor source. Since the body’s food currency is in calories, not grams or food weight, nutrient density by calorie is a better way of making assessments. Our body monitors how much energy we eat, not how much weight (of food) we eat. We only have about 2,000 calories in the calorie bank to spend every day; so, to maximize our nutrient purchase, we want to eat the most nutrient-dense foods.

To look for trends in nutrient density by calorie, we can rank the foods in the chart from best to worst, which you can see at the 3:47 minute mark of the video.

The clear winners are unprocessed, unrefined, plant-derived foods, including vegetables, herbs and spices, fruit, mushrooms, legumes, whole grains, and nuts and seeds. In general, these foods lack the disease-promoting components we want to avoid and, as the Dietary Guidelines Committee states, “These foods contain not only the essential vitamins and minerals…but also hundreds of naturally-occurring phytonutrients…that may protect against cancer, heart disease, osteoporosis, and other chronic health conditions.” So, these foods also contain hundreds of phytonutrients found in whole plant foods that are largely missing from processed and animal-derived foods. Additionally, the lack of disease-preventing compounds may be compounded by the presence of disease-promoting compounds.

So this is why people eating more plant-based tend to end up eating a more nutrient-dense dietary pattern, closer to the federal dietary recommendations. The more plant-based we get, apparently, the better.


For more information on the best diet to maximize nutrient intake while minimizing the intake of harmful food components, check out my video What Is the Healthiest Diet?.  How low should one try to push their intake of some of the food components to avoid? See Trans Fat, Saturated Fat, and Cholesterol: Tolerable Upper Intake of Zero, How Much Added Sugar Is Too Much?, and, for sodium, High Blood Pressure May Be a Choice. Surprised that trans fats weren’t limited to partially hydrogenated junk? Check out Trans Fat in Meat and Dairy

And for an overview on why I do this work to publish the latest in health and nutrition, see my introductory series

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:

Plant versus Animal Iron

It is commonly thought that those who eat plant-based diets may be more prone to iron deficiency, but it turns out that they’re no more likely to suffer from iron deficiency anemia than anybody else. This may be because not only do those eating meat-free diets tend to get more fiber, magnesium, and vitamins like A, C, and E, but they also get more iron.

The iron found predominantly in plants is non-heme iron, which isn’t absorbed as well as the heme iron found in blood and muscle, but this may be a good thing. As seen in my video, The Safety of Heme vs. Non-Heme Iron, avoidance of heme iron may be one of the key elements of plant-based protection against metabolic syndrome, and may also be beneficial in lowering the risk from other chronic diseases such as heart disease.

The data linking coronary heart disease and the intake of iron, in general, has been mixed. This inconsistency of evidence may be because of where the iron comes from. The majority of total dietary iron is non-heme iron, coming mostly from plants. So, total iron intake is associated with lower heart disease risk, but iron intake from meat is associated with significantly higher risk for heart disease. This is thought to be because iron can act as a pro-oxidant, contributing to the development of atherosclerosis by oxidizing cholesterol with free radicals. The risk has been quantified as a 27% increase in coronary heart disease risk for every 1 milligram of heme iron consumed daily.

The same has been found for stroke risk. The studies on iron intake and stroke have had conflicting results, but that may be because they had never separated out heme iron from non-heme iron… until now. Researchers found that the intake of meat (heme) iron, but not plant (non-heme) iron, was associated with an increased risk of stroke.

The researchers also found that higher intake of heme iron—but not total or plant (non-heme) iron—was significantly associated with greater risk for type 2 diabetes. There may be a 16% increase in risk for type 2 diabetes for every 1 milligram of heme iron consumed daily.

The same has also been found for cancer, with up to 12% increased risk for every milligram of daily heme iron exposure. In fact, we can actually tell how much meat someone is eating by looking at their tumors. To characterize the mechanisms underlying meat-related lung cancer development, researchers asked lung cancer patients how much meat they ate and examined the gene expression patterns in their tumors. They identified a signature pattern of heme-related gene expression. Although they looked specifically at lung cancer, they expect these meat-related gene expression changes may occur in other cancers as well.

We do need to get enough iron, but only about 3% of premenopausal white women have iron deficiency anemia these days. However, the rates are worse in African and Mexican Americans. Taking into account our leading killers—heart disease, cancer, and diabetes—the healthiest source of iron appears to be non-heme iron, found naturally in abundance in whole grains, beans, split peas, chickpeas, lentils, dark green leafy vegetables, dried fruits, nuts, and seeds.

But how much money can be made on beans, though? The processed food industry came up with a blood-based crisp bread, made out of rye flour and blood from cattle and pigs, which is one of the most concentrated sources of heme iron, about two-thirds more than blood from chickens. If blood-based crackers don’t sound particularly appetizing, you can always snack on cow blood cookies. And there are always blood-filled biscuits, whose filling has been described as “a dark-colored, chocolate flavored paste with a very pleasant taste.” (It’s dark-colored because spray-dried pig blood can have a darkening effect on the food product’s color.) The worry is not the color or taste, it’s the heme iron, which, because of its potential cancer risk, is not considered safe to add to foods intended for the general population.

Previously, I’ve touched on the double-edged iron sword in Risk Associated With Iron Supplements and Phytates for the Prevention of Cancer. It may also help answer Why Was Heart Disease Rare in the Mediterranean?

Those eating plant-based diets get more of most nutrients since whole plant foods are so nutrient dense. See Nutrient-Dense Approach to Weight Management.

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: