What RFK Jr. Doesn’t Specify: How to Take Vitamins

While Health and Human Services Secretary RFK Jr. touts the unproven power of vitamin supplements, experts warn to watch how much you take and what you take them with. Kennedy’s urging omits two important issues: the possible adverse effects of overdosing and the fact that, taken together, some vitamins and minerals invalidate one another.

Nutrients are vital but not benign. For example, the USDA Daily Recommended Intake (DRI) of Vitamin C protects against the vitamin-deficiency disease scurvy. But, as the Mayo Clinic notes, large doses of Vitamin C supplements can cause a whole list of ugly outcomes ranging from gastric upset to kidney stones.

Ditto for Vitamin A which, in recommended doses, boosts immunity and helps keep skin and hair healthy. Megadose, though, may produce headaches, rapid heartbeat, and gastric upset, all contributing to yet another overdose symptom: irritability.

More to the point, the list of nutrients that invalidate one another is clear. Start with Vitamin C and Vitamin B12. The first is acidic and may degrade the second on contact. The workaround appears to be taking them in alphabetical order: the B first and two hours later the C.

Moving on to minerals, the big bad guy is calcium. Whether as a supplement or in dairy foods such as milk and cheese, leafy greens, and (who knew?) canned fish, calcium interferes with the body’s ability to absorb iron, an especially consequential situation for anyone taking iron pills to ameliorate anemia.

Calcium and bone-building magnesium compete for absorption in the gastro tract system, which means taking them together in high doses may trigger bloating and/or diarrhea. Ditto for zinc, which boosts wound healing by strengthening the immune system. Again, the workaround is taking them separately, starting with the calcium-rich milk on your cereal at breakfast.

As with everything in life, there’s also an equal and opposite situation: Some nutrient combos enhance one another. The sterling example is iron plus Vitamin C, whose acidity increases the body’s ability to absorb iron, especially the non-heme (non-blood) iron found in plant foods such as beans and various veggies, which is why healthcare providers prescribing iron supplements usually add a C pill as well. Vitamins D and K step up calcium absorption to support bone health.

Dietitians note that whether you’re taking the pills with a meal or with water can affect your ability to get the most nutritional value. For example, fat-soluble vitamins including Vitamins A, D, E, and K are stored in fatty tissue and absorbed more easily when taken with dietary fat such as a cheese sandwich, avocados, eggs, or even full-fat ice cream. Water-soluble vitamins, including the B family and Vitamin C, are stored in water-based tissues such as blood and cells. They work best when taken with water and food. To even out the issues, the general rule is a multi-vitamin with a complete meal that has a bit of everything.

After all that, one caution remains: Supplements are serious business. According to data from the 2023 CRN (Council for Responsible Nutrition) Consumer Survey on Dietary Supplements, 74 percent of US adults take dietary supplements, and 55 percent qualify as “regular users” of these large-dose single-nutrient products.

However, in addition to interacting with one another, some nutrients interact with medical drugs, a situation most likely with supplements. For example, some patients with heart disease take warfarin, an anti-clotting med, to keep blood flowing smoothly through their arteries. Adding large doses of Vitamin E may increase the anti-clotting factor, leading to unwelcome bleeding.

There are other such interactions as well, so before doing your own prescribing, check with your doctor to be sure the combos you propose are both safe and healthful.