Vitamin Supplements: Should You or Shouldn't You? Part 2: Is there a downside to taking multivitamins?

Despite marketing claims, vitamin supplements’ only proven function is correcting vitamin deficiency. But are we risking anything by taking a multi-vitamin, just in case?

Surprising negative outcomes of vitamin supplement treatment in clinical trials

I alluded last week to studies correlating vitamin intake with bad outcomes. I'll mention just a few:

A very large meta-analysis, including 68 randomized trials, and 232,606 participants looking at antioxidant vitamin supplements’ effectiveness, found that treatment with beta carotene, vitamin A, and vitamin E had no significant effects on gastrointestinal cancers and may also increase mortality.

A recent double-blind, placebo-controlled, trial including 1,021 men and women looked at whether high-dose folic acid supplements (1,000 micrograms, about 2.5 times the recommended daily dose) could prevent new polyps in people with a recent history of colorectal polyps. Folic acid treatment was associated with higher risks of having 3 or more adenomas and of non-colorectal cancers.

While many trials are ongoing, and this issue is far from resolved, studies such as these have dampened the enthusiasm for vitamins among experts, and resulted in a more skeptical approach toward them.

Vitamin overdose

Although vitamins are safe at a very wide range of doses, and it’s practically impossible to overdose on vitamins that occur naturally in food, there is an upper safe limit for vitamins from supplements, and most experts warn not to take vitamins in large doses.

The fat-soluble vitamins (A, D, E, and K) have a higher potential for toxicity than the water soluble ones. For instance, Vitamin A overdose can manifest in headaches, liver damage, dry skin, bone loss etc. Large doses of Vitamin A are also highly teratogenic (that is, they cause malformations to the embryo). Vitamin D toxicity may manifest as nausea, constipation alternating with diarrhea, vomiting, pain in the joints, loss of appetite and irreversible calcium deposits in various organs. Most of the excess of water soluble vitamins is excreted (that’s why vitamin supplements are dubbed ‘fish food’ or ‘expensive urine’). But even the innocent seeming water-soluble Vitamin C, which many people take in doses that are multiples of the recommended daily allowance (in the unfounded belief it prevents colds) can have untoward effects, and cause kidney stones, diarrhea and nausea in large doses.

And, most of us need to bear in mind that many processed foods are fortified or enriched with synthetic vitamins, so if you also take vitamin supplements the possibility of overdosing is real.

Are vitamin supplements a viable nutritional safety net, and is having one a good idea?

I contemplate this question in the frantic race to get my kids to school on time. They regularly get up late, and there’s the inevitable rush to make sure they have everything they need for their day. I’m sure that if they thought there’d actually be consequences of their tardiness and inefficiency, they would learn to be more responsible, and I’d achieve a larger goal than just having them at school on time.

I hear that some drivers are aware of how advanced new cars have become, and trust the cars’ ability to take over and prevent skidding and loss of control, to the point they don’t feel the need to be that careful.

The knowledge that you have a safety net with your daily multivitamin has led to a similar attitude of complacency, with some people believing that it’s not that important to eat well, as we’re guaranteed nourishment from the pill. The fact is, no pill or food fortification scheme is likely to ever adequately substitute for a healthy diet.

It’s easy to get enough vitamins from food if you maintain a reasonably healthy diet. Eating a diet that includes a few more fruits and vegetables will provide the safety net, and at a lower cost. On the other hand you’re kidding yourself if you think that taking a pill will correct the damage of poor eating habits. Multi-vitamins do not have the same beneficial qualities as the nutrients from foods, and if taking vitamins is giving you an excuse to eat badly, your safety net is full of holes. Although you get some benefit to address overt vitamin deficiency, the many benefits of eating a healthy diet will be missed by relying on multi-vitamins.

Next week I'll conclude the vitamin discussion series with my strong belief that real food is the best source of nutrients.
Dr. Ayala