Vitamin D Supplements for Reducing Cancer Mortality

It all started with a famous study entitled “Do sunlight and vitamin D reduce the likelihood of colon cancer?” that was published in 1980. Johns Hopkins University researchers were trying to figure out why states like New Mexico and Arizona have only about half the colon cancer rates of states like New York, New Hampshire, and Vermont. Could it be because New Mexicans and Arizonans get so much more sun? The researchers proposed that perhaps vitamin D, known as the sunshine vitamin, is a protective factor against colon cancer. Since then, sun exposure has also been associated with lower rates of 14 other types of cancer.

As I discuss in my video Do Vitamin D Supplements Reduce the Risk of Dying from Cancer?, vitamin D may also affect cancer survival. Higher blood levels of vitamin D were associated with lower mortality of patients with colorectal cancer. How much lower? Nearly half the mortality. And, the higher the vitamin D levels, the lower the death rate appeared to fall. This may explain why the survival rate from colon cancer may depend in part “on the season of diagnosis.” The risk of rapid death is lowest if you’re diagnosed in the fall after you’ve spent the summer building up your vitamin D stores. Other risk factors could be seasonal, too. For example, perhaps people are taking advantage of the fall harvest and eating healthier, which might explain lower risk in the autumn. Additionally, “[a]lcohol intake is a risk factor and may be highest in the winter season…” What about physical activity? In the summer, we may be more likely to be outside running around, not only getting more sun, but also getting more exercise, which may itself be protective.

These kinds of studies just provide circumstantial evidence. Establishing a cause-and-effect relationship between colon cancer and vitamin D deficiency using observational studies is challenging because of confounding factors, such as exercise habits—so-called lurking variables. For example, there may be a tight correlation between ice cream sales and drowning deaths, but that doesn’t mean ice cream causes drowning. A more likely explanation is that there is a lurking third variable, like hot weather in summertime, that explains why drowning deaths are highest when ice cream consumption is also at its highest.

This actually happened with hormone replacement therapy. Women taking drugs like Premarin appeared to have 50 percent less risk of heart disease, so doctors prescribed it to women by the millions. But, if we dig a little deeper into the data, we find that, indeed, women taking estrogen had 50 percent lower risk of dying from heart disease, but they also had a 50 percent lower risk of dying from accidents and homicide, so it probably wasn’t the drug. The only way to know for sure is to put it to the test in a randomized, clinical trial, where half the women are given the drug and we see what happens. A decade later, such a study was done. Instead of having a 50 percent drop in risk, within a year of being given the hormone pills, heart attack and death rates shot up 50 percent. In retrospect, the lurking variable was likely socioeconomic class. Poor women are less likely to be prescribed hormone replacement therapy and more likely to be murdered and die of heart disease. Because of the lurking variable, a drug we now know to be dangerous had initially appeared to be protective.

Besides lurking variables, there’s also the possibility of reverse causation. Perhaps low vitamin D levels didn’t worsen the cancer. Instead, maybe the cancer worsened the vitamin D levels. This may be unlikely, since tumors don’t appear to directly affect vitamin D levels, but cancer treatment might. Even simple knee surgery can cause vitamin D levels to drop dramatically within hours, thought to be due simply to the inflammatory insult of cutting into someone. So, maybe that could help explain the link between lower vitamin D and lower survival. And, cancer patients may be spending less time running around the beach. So, yes: Higher vitamin D levels are associated with improved survival in colorectal cancer, and the same has been found for breast cancer. In fact, there is about double the risk of breast cancer recurrence and death in women with the lowest vitamin D levels. What’s more, higher vitamin D levels are associated with longer survival with ovarian cancer, as well as having better outcomes for other cancers like lymphoma. But, the bottom-line, as we learned with hormone replacement, is that we have to put it to the test. There weren’t a lot of randomized controlled trials on vitamin D supplements and cancer, however…until now.

We now have a few randomized controlled trials, and vitamin D supplements do indeed appear to reduce the risk of dying from cancer! What dose? Researchers suggest getting blood levels up to at least about 75 nanomoles per liter. These levels are not reached by as many as three-quarters of women with breast cancer nor achieved by a striking 97 percent of colon cancer patients .

Getting up to these kinds of levels—75 or, perhaps even better, 100 nanomoles—might require about 2000 to 4000 IU of vitamin D a day, levels of intake for which there appear to be no credible evidence of harm. Regardless of what the exact level is, the findings of these kinds of studies may have a profound influence on future cancer treatment.


What about just getting sun instead? Be sure to check out my six-part video series:

It’s better, of course, to prevent colon cancer in the first place. See, for example:

For more on that extraordinary story about Premarin and hormone replacement therapy, see How Did Doctors Not Know About the Risks of Hormone Therapy?

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:

The Answer to a Colon Cancer Mystery

Colorectal cancer is the third most common cause of cancer death in the world. Thankfully, the good bacteria in our gut take the fiber we eat and make short-chain fatty acids, like butyrate, that protect us from cancer. We take care of them, and they take care of us. If we do nothing to colon cancer cells, they grow. That’s what cancer does. But if we expose the colon cancer cells to the concentration of butyrate our good bacteria make in our gut when we eat fiber, the growth is stopped in its tracks. If, however, the butyrate stops, if we eat healthy for only one day and then turn off the fiber the next, the cancer can resume its growth. So, ideally, we have to eat a lot of fiber-rich foods—meaning whole plant foods—every day.

What about the populations, like those in modern sub-Saharan Africa, where they don’t eat a lot of fiber yet still rarely get colon cancer? Traditionallly. they used to eat a lot of fiber, but now their diet is centered around highly refined corn meal, which is low in fiber—yet they still have low colon cancer rates. Why? This was explained by the fact that while they may be lacking protective factors like fiber, they are also lacking cancer-promoting factors like animal protein and fat. But are they really lacking protective factors?

If you measure the pH of their stools, the black populations in South Africa have lower pH, which means more acidic stools, despite comparable fiber intakes. That’s a good thing and may account for the lower cancer rates. But, wait a second. Low colon pH is caused by short-chain fatty acids, which are produced by our good bacteria when they eat fiber, but they weren’t eating any more fiber, suggesting there was something else in addition to fiber in their diets that was feeding their flora. And, indeed, despite low fiber intake, the bacteria in their colon were still churning out short-chain fatty acids like crazy. But if their bacteria weren’t eating fiber, what were they eating? Resistant starch. “[T]he method of cooking and eating the maize [corn] meal as a porridge results in an increase in resistant starch, which acts in the same way as fiber in the colon,” as a prebiotic, a food for our good bacteria to produce the same cancer-preventing, short-chain fatty acids.

As I discuss in my video Resistant Starch and Colon Cancer, “[r]esistant starch is any starch…that is not digested and absorbed in the upper digestive tract [our small intestine] and, so, passes into the large bowel,” our colon, to feed our good bacteria. When you boil starches and then let them cool, some of the starch can recrystallize into a form resistant to our digestive enzymes. So, we can get resistant starch eating cooled starches, such as pasta salad, potato salad, or cold cornmeal porridge. “This may explain the striking differences in colon cancer rates.” Thus, they were feeding their good bacteria after all, but just with lots of starch rather than fiber. “Consequently, a high carbohydrate diet may act in the same way as a high fiber diet.” Because a small fraction of the carbs make it down to our colon, the more carbs we eat, the more butyrate our gut bacteria can produce.

Indeed, countries where people eat the most starch have some of the lowest colon cancer rates, so fiber may not be the only protective factor. Only about 5 percent of starch may reach the colon, compared to 100 percent of the fiber, but we eat up to ten times more starch than fiber, so it can potentially play a significant role feeding our flora.

So, the protection Africans enjoy from cancer may be two-fold: a diet high in resistant starch and low in animal products. Just eating more resistant starch isn’t enough. Meat contains or contributes to the production of presumed carcinogens, such as N-nitroso compounds. A study divided people into three groups: one was on a low-meat diet, the second was on a high-meat diet including beef, pork, and poultry, and the third group was on the same high-meat diet but with the addition of lots of resistant starch. The high-meat groups had three times more of these presumptive carcinogens and twice the ammonia in their stool than the low-meat group, and the addition of the resistant starch didn’t seem to help. This confirms that “exposure to these compounds is increased with meat intake,” and 90 percent are created in our bowel. So, it doesn’t matter if we get nitrite-free, uncured fresh meat; these nitrosamines are created from the meat as it sits in our colon. This “may help explain the higher incidence of large bowel cancer in meat-eating populations,” along with the increase in ammonia—neither of which could be helped by just adding resistant starch on top of the meat.

“[T]he deleterious effects of animal products on colonic metabolism override the potentially beneficial effects of other protective nutrients.” So, we should do a combination of less meat and more whole plant foods, along with exercise, not only for our colon, but also for general health.


This is a follow-up to my video Is the Fiber Theory Wrong?.

What exactly is butyrate? See:

For videos on optimizing your gut flora, see:

Interested in more on preventing colon cancer? See:

If you’re eating healthfully, do you need a colonoscopy? Find out in Should We All Get Colonoscopies Starting at Age 50?.

When regular starches are cooked and then cooled, some of the starch recrystallizes into resistant starch. For this reason, pasta salad can be healthier than hot pasta, and potato salad can be healthier than a baked potato. Find out more in my video Getting Starch to Take the Path of Most Resistance.

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’s the Secret to Latino Longevity?

Latinos living in the United States tend to have “less education, a higher poverty rate, and worse access to health care” and “represent the ultimate paradigm of healthcare disparities,” with the highest rate of uninsured, lowest rates of health screening and counseling, and poorest levels of blood pressure and blood sugar control, as well as “other measures of deficient quality of care.” So they must have dismal public health statistics, right? According to the latest national data, the life expectancy of white men and women is 76 and 81 years, respectively, and that of black men and women is shorter by a handful of years. And Latinos? Amazingly, they beat out everyone.

Latinos live the longest.

This has been called the Hispanic Paradox (now also known as the Latino Paradox), which I explore in my video, The Hispanic Paradox: Why Do Latinos Live Longer?. Latinos have a 24 percent lower risk of premature death and “lower risks of nine of the leading 15 causes of death,” with notably less cancer and heart disease. This was first noticed 30 years ago but was understandably was met with great criticism. Maybe the data were unreliable? No, that didn’t seem to be it. Maybe only the healthiest people migrate? Turns out the opposite may be true. What about the “salmon bias” theory, which “proposes that Latinos return to their home country…to ‘die in their home’” so they aren’t counted in U.S. death statistics? That theory didn’t pan out either.

Systematic reviews “confirm the existence of a Hispanic Paradox.” Given the strong evidence, it may be time to accept it and move on to figuring out the cause. The very existence of the “Hispanic Paradox” could represent “a major opportunity to identify a protective factor for CVD [cardiovascular disease] applicable to the rest of the population.” After all, whatever is going on “is strong enough to overcome the disadvantageous effect” of poverty, language barriers, and low levels of education, health literacy, quality of healthcare, and insurance coverage. Before we get our hopes up too much, though, could it just be genetic? No. As foreign-born Latinos acculturate to the United States, as they embrace the American way of life, their mortality rates go up. So, what positive health behaviors may account for Latino longevity?

Perhaps they exercise more? No, Latinos appear to be even more sedentary. They do smoke less, however the paradox persists even after taking that into account. Could it be their diet? As they acculturate, they start eating more processed and animal-based foods, and consume fewer plant foods—and perhaps one plant food in particular: beans. Maybe a reason Latinos live longer is because they eat more beans. Although Latinos only represent about 10 percent of the population, they eat a third of the beans in the United States, individually eating four to five times more beans per capita, a few pounds a month as opposed to a few pounds per year. That may help explain the “Hispanic Paradox,” because legumes (beans, split peas, chickpeas, and lentils) cool down systemic inflammation.

In my video, you can see the mechanism researchers propose in terms of lung health. While cigarette smoking and air pollution cause lung inflammation, which increases the risk for emphysema and lung cancer, when we eat beans, the good bacteria in our gut take the fiber and resistant starch, and form small chain fatty acids that are absorbed back into our system and decrease systemic inflammation, which not only may inhibit lung cancer development, but also other cancers throughout the body. Latinos have the lowest rates of chronic obstructive pulmonary disease (COPD) and lung cancer, and also tend to have lower rates of bladder cancer, throat cancer, and colorectal cancer for both men and women.

This “systemic inflammation” concept is also supported by the fact that when Latinos do get cardiovascular disease or lung, colon, or breast cancer, they have improved survival rates. Decreasing whole body inflammation may be important for both prevention and survival.

Asian Americans also appear to have some protection, which may be because they eat more beans, too, particularly in the form of tofu and other soy foods, as soy intake is associated with both preventing lung cancer and surviving it.

Hispanics also eat more corn, tomatoes, and chili peppers. A quarter of the diet in Mexico is made up of corn tortillas, and Mexican-Americans, whether born in Mexico or the United States, continue to eat more than the general population. Looking at cancer rates around the world, not only was bean consumption associated with less colon, breast, and prostate cancer, but consumption of rice and corn appeared protectively correlated, too.

Since NAFTA, though, the North American Free Trade Agreement, the Mexican diet has changed to incorporate more soda and processed and animal foods, and their obesity rates are fast catching up to those in the United States.

In the United States, Latinos eat more fruits and vegetables than other groups, about six or seven servings a day, but still don’t even make the recommended minimum of nine daily servings, so their diet could stand some improvement. Yes, Hispanics may only have half the odds of dying from heart disease, but it’s “still the number one cause of death among Hispanics. Therefore, the current results should not be misinterpreted to mean that CVD is rare among Hispanics.” Ideally they’d be eating even more whole plant foods, but one thing everyone can learn from the Latino experience is that a shift toward a more plant-based diet in general can be a potent tool in the treatment and prevention of chronic disease.


Data like this support my Daily Dozen recommendation for eating legumes ideally at every meal, and we have free apps for both iPhone and Android that can help you meet these dietary goals.

For more on the wonders of beans, split peas, chickpeas, and lentils, see my videos and love your legumes!:

What’s the best way to eat them? See Canned Beans or Cooked Beans? and Cooked Beans or Sprouted Beans?.

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: