Too Much of This Vitamin May Raise Cancer Risk, New Study Says

Reviewed by Dietitian Emily Lachtrupp, M.S., RD

Key Points

Vitamin A is crucial for maintaining healthy vision, a robust immune system and radiant skin. There are also some carotenoids with provitamin A activity—meaning they get converted to vitamin A in your body. Those vitamin A functions as an antioxidant, reducing oxidative stress and inflammation. In addition, there’s evidence that vitamin A plays a role in cancer prevention. But how much is enough? And can too much be, well, too much?

Researchers wanted to know, too, so they conducted a hospital-based case-control study with Vietnamese participants. They published their findings in Nutrients. Let’s break down what they found.

How Was This Study Conducted?

Researchers recruited participants from four major university hospitals in Vietnam. There were two groups of participants. One group was made up of over 3,700 cancer patients; the other was almost 3,000 control patients who did not have cancer, but were admitted to the hospital for other reasons. The cancer group included patients with esophageal, stomach, colon, rectal, lung, breast and other cancers.

Demographic information was gathered, as was dietary information using a food frequency questionnaire. From this info, participants’ dietary intake of vitamin A was calculated.

What Did This Study Find?

After running several statistical analyses, including adjusting for confounding factors, like sex, age and BMI, researchers found a U-shaped association between vitamin A intake and cancer. This means that both the lowest and highest intakes of vitamin A were associated with an increase in cancer risk. The reference vitamin A intake was 85.3-104 mcg/day; this reference marks the average intake for the control group, which had no cancer.

The cancers that were most strongly associated with vitamin A were esophageal, breast, rectum and stomach—but not colon.

This study does have several limitations, starting with the potential for recall bias for the food frequency questionnaire—because, let’s face it, most of us can’t remember what we ate yesterday, let alone try to estimate how much of certain foods we eat on a regular basis. Also, because this was a hospital-based study, it might not be generalizable to other populations, nor can we be certain it applies to other ethnicities.

How Does This Apply to Real Life?

As with most things in life, more is not necessarily better when it comes to vitamin A. But you also need to make sure you’re getting enough of this vitamin, because when you hit the sweet spot with it, it’s a nutritional powerhouse. These study authors do not provide an amount they recommend; they only provide the reference intake amount.

According to the U.S. National Institutes of Health (NIH), the recommended vitamin A intake shifts based on your age and sex. And since you can get vitamin A from so many sources, recommendations are given in retinol activity equivalents (RAE), which can be translated to certain amounts of beta-carotene, retinol and other forms of vitamin A. Here’s how the recommendations break down for adults:

Foods rich in vitamin A include carrots, pumpkins, sweet potatoes, spinach, tuna and beef liver. We love that it’s fun to get creative with these ingredients, like we do in our Sheet-Pan Carrots & Chickpeas with Tahini, Pumpkin Trifle and Tuna Niçoise Melt. And the good news is that most Americans are getting enough vitamin A in their diets, so you may find that you’re already in good shape when it comes to this nutrient.

Of course, vitamin A isn’t the only important nutrient for cancer prevention, nor is diet the only area that needs attention. And since cancer rates are on the rise, including in young people, now is the time to start prevention strategies.

The American Cancer Society suggests that the major areas of concern regarding cancer risk that we have control over include diet, physical activity, tobacco use and alcohol intake. Regarding diet, an anti-inflammatory eating pattern is recommended, as it’s loaded with nutrient-dense foods, like fruits, vegetables, nuts, seeds, whole grains and healthy fats.

Engaging in regular physical activity can also reduce your cancer risk, including for breast cancer. And more and more evidence is stacking up against alcohol and tobacco products.

Our Expert Take

This study suggests that too much and too little vitamin A may raise your risk of several types of cancer. If you’re unsure whether you’re getting the right amount of this essential vitamin, make an appointment to talk with a registered dietitian or seek out a healthcare professional for advice.

It’s also important to take a whole-health approach to cancer prevention by eating lots of anti-inflammatory foods, moving your body more often, getting plenty of quality sleep, managing your stressors, limiting or avoiding alcohol and avoiding tobacco products. If this list overwhelms you, choose one area to start working on and be consistent with it. Before long, you’ll realize the other areas come easier. And while there’s no guarantee you’ll prevent cancer with this strategy, if you do get it, you’ll be stronger and better able to handle what it throws at you.

Read the original article on EatingWell