Which supplements are bad for you

But studies suggest that when taken in excess, antioxidants can actually be harmful. A large, long-term study of male smokers found that those who regularly took Vitamin A were more likely to get lung cancer than those who didn't.

And a review of trials of several different types of antioxidant supplements put it this way: "Treatment with beta carotene, vitamin A, and vitamin E may increase mortality.

Vitamin C: Skip it - it probably won't help you get over your cold, and you can eat citrus fruits instead. The Vitamin C hype - which started with a suggestion from chemist Linus Pauling made in the s and has peaked with Airborne and Emergen-C - is just that: hype.

Study after study has shown that Vitamin C does little to nothing to prevent the common cold. Plus, megadoses of 2, milligrams or more can raise your risk of painful kidney stones. For years, Vitamin B3 was promoted to treat everything from Alzheimer's to heart disease. But recent studies have called for an end to the over-prescription of the nutrient.

A large study of more than 25, people with heart disease found that putting people on long-acting doses of Vitamin B3 to raise their levels of 'good', or HDL, cholesterol didn't reduce the incidence of heart attacks, strokes, or deaths. Plus, people in the study who took the B3 supplements were more likely than those taking a placebo to develop infections, liver problems, and internal bleeding.

Probiotics: Skip them - the science isn't advanced enough yet for them to have a significant benefit, and you can eat yogurt instead. The idea behind them is simple: Support the trillions of bacteria blossoming in our gut which we know play a crucial role in regulating our health. So far, the effects of probiotics have been all over the map. Sometimes they help, sometimes they don't. Medications that could potentially be affected include statins , which are used to control cholesterol, and a number of antidepressants and anti-seizure medications.

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But they bore little fruit. In the s and into the 80s, for example, many mice — our go-to laboratory animal — were prescribed a variety of supplementary antioxidants in their diet or via an injection straight into the bloodstream.

Some were even genetically modified so that the genes coding for certain antioxidants were more active than non-modified lab mice. Far from protecting us from disease, one study found that vitamin supplements increased the incidence of lung cancer among smokers Credit: Alamy.

What about humans? But what they can do is set up long-term clinical trials. The premise is pretty simple. First, find a group of people similar in age, location, and lifestyle. Second, split them into two subgroups. Third, and crucially to avoid unintentional bias, no one knows who was given which until after the trial; not even those administering the treatment.

Known as a double-blind control trial, this is the gold standard of pharmaceutical research. Since the s, there have been many trials like this trying to figure out what antioxidant supplementation does for our health and survival. The results are far from heartening. In , for example, one trial followed the lives of 29, Finish people in their 50s.

All smoked, but only some were given beta-carotene supplements. A similar result was found in postmenopausal women in the U. It gets worse. One study of more than 1, heavy smokers published in had to be terminated nearly two years early. Compared to placebo, 20 more people were dying every year when taking these two supplements.

Over the four years of the trial, that equates to 80 more deaths. But, according a review from that noted the conclusions of 27 clinical trials assessing the efficacy of a variety of antioxidants, the weight of evidence does not fall in its favour. Just seven studies reported that supplementation led to some sort of health benefit from antioxidant supplements, including reduced risk of coronary heart disease and pancreatic cancer.

That left another 10 studies that found many patients to be in a measurably worse state after being administered antioxidants than before, including an increased incidence of diseases such as lung and breast cancer.

Linus Pauling was largely unaware of the fact that his own ideas could be fatal. In , before the publication of many of the large-scale clinical trials, he died of prostate cancer. But did it contribute to a heightened risk? Dosing up on vitamin C does not even help us fight the common cold Credit: Alamy. Ever since Harman proposed his great theory of free radicals and ageing, the neat separation of antioxidants and free radicals oxidants has been deteriorating. It has aged. Antioxidant is only a name, not a fixed definition of nature.

At the correct dose, vitamin C neutralises highly charged free radicals by accepting their free electron. But by accepting an electron, the vitamin C becomes a free radical itself, able to damage cell membranes, proteins and DNA. Although such simplifying of complex biochemistry is in itself problematic, the clinical trials above provide some possible outcomes.

Antioxidants have a dark side.