‘Are vitamins killing you?’ — the latest instalment in TV3’s documentary series Inside New Zealand, broadcast October 28 — certainly grabbed our attention at the Science Media Centre this week. Although the title was a little dramatic, the programme did convey an important message: that excess intakes of vitamins can be harmful.
The programme makers followed eight supplement-users over a period of six weeks. At the start of the programme seven of the subjects ceased to take their supplements, and one changed from taking bee pollen to taking a multi-vitamin supplement (the control).
It was no surprise that initial blood tests demonstrated high levels of some vitamins in some subjects. After the six-week trial period, those who had ceased to take the supplements found the vitamin levels in their blood generally returning to normal levels.
With the exception of vitamin D, which was low in some of the subjects, no one was deficient in any vitamin. They were a health-conscious group of people who seemed to be eating a healthy, varied and nutritionally adequate diet.
It was great to see experts like Associate Professor Winsome Parnell from the University of Otago on the programme, highlighting the fact that for most people, the ideal way to get nutrients is from food. Winsome commented that we should in particular avoid taking multiple sources of the fat-soluble vitamins, such as vitamin A, which is stored in the liver and may have adverse effects in the long term.
Professor Rod Jackson from Auckland University was so concerned about people taking vitamin supplements when they are not needed that he suggested such supplements should be available on prescription only.
This issue is not new and there have been concerns among health professionals for some time that high intakes of some vitamins could have adverse effects. In fact, a study published in 1994 in the New England Journal of Medicine found that total mortality was 8% higher among male smokers who received beta-carotene supplements, than among those who did not, raising the possibility that the supplements may have harmful effects.
A UK Department of Health Report in 1998 on the Nutritional Aspects of the Development of Cancer suggested that a change in the usual balance of carotenoids (for example, when people take high-dose purified supplements) might lead to potentially adverse effects in relation to their absorption, metabolism and function. The Working Group who compiled the report recommended the avoidance of beta-carotene supplements as a way of protecting against cancer and advised caution in the use of high-dose purified supplements of other nutrients as they can’t be assumed to be safe.
More recent research, published in the Journal of the American Medical Association in 2007, and in a Cochrane Review published last year, assessed the effect of antioxidant supplements on mortality in randomised primary and secondary prevention trials. There was no evidence to support the use of antioxidant supplements to prevent mortality in healthy people or in patients with various diseases. In fact, results showed that treatment with beta-carotene, vitamin A and vitamin E may increase mortality. The potential effects of vitamin C and selenium need more study.
The New Zealand Food and Nutrition Guidelines for Healthy Adults (by the Ministry of Health) recommend that the best nutrition strategy for promoting optimal health and preventing disease is to eat well by including a wide variety of nutritious foods in the diet. According to these guidelines, vitamin and mineral supplements are only appropriate in specific circumstances, preferably on the advice of a health professional. The groups of people who do need supplements include, for example: people with a diagnosed deficiency of a nutrient, who should take a supplement providing that nutrient; women in the early stages of pregnancy, who need a folic acid supplement; and strict vegans, who need vitamin B12 supplements.
However, just because a small amount of a vitamin found in a food is essential for optimal physiological functioning does not mean that packaging up individual nutrients into a tablet at levels above the recommended intake is going to be even better. The message from the programme last night was that, in general, we should be getting all our nutrients from a healthy balanced diet. And I agree. My advice is that for most of us a varied diet should provide us with all the nutrients we need. For those people who do take a supplement, I’d recommend avoiding mega-dosing and avoiding taking several supplements together, as the cumulative effect could result in toxic intakes.
Perhaps, as Professor Jackson suggests, it is now timely to look at tighter regulations on the sale of vitamins and minerals.