Then I found out that higher intake of vitamin A was associated with an increased risk of hip fractures in postmenopausal women like me, and I stopped. (High doses of vitamin A also cause births defects and are contraindicated in pregnancy.) Now I only take supplemental calcium and vitamin D, not on general principles but because of personal risk factors.
We’re being bombarded by advice to take vitamins and various other supplements. Health gurus like Andrew Weil recommend that everyone take vitamins (which they just happen to sell). The orthomolecular followers of Linus Pauling want us to take megadoses of vitamins. Ray Kurzweil tells us we should take vitamins to make us live longer; he takes 250 vitamin and supplement pills a day and thinks he will live forever. (You can read about his ideas in his book Fantastic Voyage: Live Long Enough to Live Forever.) Who should we believe?
I don’t get my medical information from popular sources. I rely on primary sources and on secondary sources that I have come to trust to accurately represent the current state of the peer-reviewed medical literature, for instance, the American Academy of Family Physicians and The Medical Letter.
The official position of the American Academy of Family Physicians is not to recommend vitamins or other supplements for the general population. They say
The decision to provide special dietary intervention or nutrient supplementation must be on an individual basis using the family physician’s best judgment based on evidence of benefit as well as lack of harmful effects. Megadoses of certain vitamins and minerals have been proven to be harmful.
The Medical Letter is an independent unbiased source written by a group of experts who review all the literature and provide periodic updates. Their most recent review of vitamin supplements (Vol 47 No 1213, p.57-8, July 18, 2005) concluded,
Supplements are necessary to assure adequate intake of folic acid in young women and possibly of vitamins D and B12 in the elderly. There is no convincing evidence that taking supplements of vitamin C prevents any disease except scurvy. Women should not take vitamin A supplements during pregnancy or after menopause. No one should take high dose beta carotene supplements. A balanced diet rich in fruits and vegetables may be safer than taking vitamin supplements. No biologically active substance taken for a long term can be assumed to be free of risk.
That’s it. That’s all science has to say about vitamins for the general population. Of course there are specific indications for individual patients with various health conditions. Patients who have had gastric bypass need large doses of vitamins. Niacin can be used therapeutically for patients with hyperlipidemia. There are lots of specific indications that your doctor knows about and can prescribe for. And if you have one of those indications, you may need a higher dose than you would get from a multivitamin.
Enthusiasts misrepresent the science. For instance, they are selling products to “prevent” age-related macular degeneration. A combination of high-dose beta-carotene, vitamin C, vitamin E, and zinc delays progression in patients who already have the disease, but there’s no evidence that it can prevent it from developing in the first place.
Beta-carotene is touted as an antioxidant, but it also has pro-oxidant effects in the body. There is good evidence that high-dose beta-carotene supplements can be harmful.
Supplemental beta-carotene may increase the risk of lung cancer, prostate cancer, intracerebral hemorrhage, and cardiovascular and total mortality in people who smoke cigarettes or have a history of high-level exposure to asbestos. Beta-carotene from foods does not seem to have this effect. In people who smoke, beta-carotene may increase cardiovascular mortality. In men who smoke and have had a prior myocardial infarction (MI or heart attack), the risk of fatal coronary heart disease increases by as much as 43% with low doses of beta-carotene. There is some evidence that beta-carotene in combination with selenium, vitamin C, and vitamin E might lower high-density lipoprotein 2 (HDL2) cholesterol levels. HDL levels are protective so this is considered to be a negative effect. Dizziness, reversible yellowing of palms, hands, or soles of feet and to a lesser extent the face (called carotenoderma) can occur with high doses of beta-carotene. Loose stools, diarrhea, unusual bleeding or bruising, and joint pain have been reported.
In addition to vitamins, we hear recommendations for all kinds of other diet supplements. There’s no good evidence for most of them. For fish oil, one of the most popular supplements, the evidence boils down to this:
(1) In patients who have had a heart attack, fish oil improves survival.
(2) It reduces triglycerides.
(3) In patients with high cholesterol levels it reduces the risk of coronary events but does not decrease mortality.
(4) It reduces blood pressure slightly.
Studies show fish oil may increase the risk of death and arrhythmias in patients with certain heart conditions, and high doses can worsen control of diabetes and can increase bleeding tendency.
The Medical Letter says,
Eating fatty fish may be beneficial for healthy people, but there is no evidence from prospective trials that fish oil supplements prevent cardiovascular disease in the general population.
I vote for leaving the fish oil in the fish.
Lots of people believe that vitamin supplements make a difference in our health and give us energy. Lots of people think taking vitamins will make you live longer. Different people believe many things; the real question is whether there is any evidence to support their beliefs.
You can find all sorts of studies and speculations suggesting that various supplements are good for you, but when you stick to rigorous science, the evidence just isn’t there. There are two philosophies: to take everything that is suggested just in case, or to wait for scientific validation before taking anything. Based on long experience, I consider the latter course more reasonable. I can’t begin to tell you how many times I’ve heard strong recommendations for something that was later shown to be useless or harmful.
One example: Vitamin E was strongly recommended to prevent heart disease and for other indications. Then they discovered that the high doses they were recommending were toxic. They lowered the dose. Then better studies showed that supplementation with vitamin E either did no good or made things worse.
More and more studies are showing that while vitamins in food are good for you, extra vitamins in pill form may not be so good. For instance, antioxidants were thought to reduce the risk of cataracts, but a 2006 study showed no effects. Then a 2008 study tested whether taking a Centrum multivitamin daily could slow the development of cataracts. They did find a reduction in “lens events” but there was no significant difference in the rate of cataract surgery or moderate visual loss, and the number of posterior subcapsular cataracts (the worst kind) doubled.
Most multivitamins contain iron, but there is evidence that lowering iron levels might be advisable. Lower body iron stores may protect against malignancy by reducing iron-induced oxidative stress.
There are some promising studies on vitamin D, but they haven’t yet translated into consensus recommendations for the general population. I’m withholding judgment; meanwhile there doesn’t seem to be any downside to taking 800-1000 IU of vitamin D a day if you want to.
There are many other things we can do to “improve our health” that don’t involve taking pills, vitamins or any other supplements. Eating a healthy diet, exercising, getting enough sleep, reducing stress, and maintaining ideal weight top my list.
Critics of medicine often pick on Big Pharma for its profit motives. How much money do you think Big Vitamin makes? How much money is being spent on unnecessary vitamins that provide no real benefit? Any excess is promptly eliminated. Are we just producing expensive urine? Are our toilets getting the benefit? Are all those vitamins in our sewage good for the environment?
One could argue that multivitamins are good for healthy sewage bacteria and healthy profits for manufacturers. But I’d rather support my own health than theirs.
This article was originally published in the Science-Based Medicine Blog.