US researchers found that people taking 400mg of vitamin E daily had a 28 per cent higher risk of lung cancer than people who did not take vitamin E supplements. The increased lung cancer risk was found to be most prominent in smokers.
The findings renew concerns over the safety of vitamin supplements and follow previous warnings about similar risks associated with excessive beta-carotene use.
In 2002, a Finnish study found that taking beta-carotene supplements was linked to an 18 per cent increased risk of developing lung cancer.
What is the research?
The reports are based on a US study into whether multivitamins, vitamin C, vitamin E or folate supplements could reduce the risk of lung cancer.
Researchers mailed health questionnaires to over 350,000 Washington State residents aged 50 to 76 years. It looked at supplement and vitamin use in the past 10 years. It also covered known risk factors for lung cancer such as smoking status, BMI and family history.
A total of 77,719 participants returned the questionnaires and were eligible for the study.
Quantity of vitamin intake was calculated.
Over four years of follow-up, diagnosed cases of lung cancer among participants were monitored using the national cancer register. During the course of the study, 521 participants developed lung cancer, including 42 non-smokers.
Vitamin E intake of 400mg daily for 10 years was associated with a 28 per cent increased risk in non-small cell lung cancer, compared with those who never took vitamin E supplements.
But no increased risk of lung cancer was seen in participants who had taken low or moderate doses of vitamin E or in those who had taken multivitamins, vitamin C or folate.
A possible mechanism for the link between vitamin E and an increased risk of lung cancer is that although vitamin E is considered an antioxidant, it might also act as a pro-oxidant, suggest the researchers.
Pro-oxidants produce oxidative stress that can cause damage to cells and tissue.
What do the researchers say?
Lead researcher Dr Christopher Slatore, from the University of Washington in Seattle, said: 'In contrast to the often assumed benefits or, at least, lack of harm, supplemental vitamin E was associated with a small increased risk of lung cancer.
'This is an interesting but not a conclusive link,' he added. 'The findings of this study need to be replicated in more human studies before we can come to a firm conclusion.'
Nevertheless, he urged patients to discuss the benefits and harms of vitamin E supplements with their doctor, especially if they smoked.
Further studies are planned that will investigate whether or not vitamin supplements and medications can increase the risk of other cancers such as those of the prostate, breast and colon, added Dr Slatore.
What do other experts say?
Henry Scowcroft, senior science information officer at Cancer Research UK, said: 'The jury is still very much out on whether vitamin and mineral supplements can affect cancer risk.
'Some studies suggest a benefit, but others show no effect and some, like this one, suggest they may even increase risk.
'Research repeatedly shows that a healthy, balanced diet can reduce your risk of some cancers while giving you all the vitamins you need.'
Quitting smoking remains the most effective way to avoid many cancers, he said, adding that no diet or vitamin supplement could counteract the toxic effects of cigarettes.
Am J Respir Crit Care Med 2008; 177: 524-30
- Long-term use of vitamin E supplements may increase the risk of lung cancer by 28 per cent.
- Lung cancer risk is most prominent among smokers.
- Patients should be advised to quit smoking to reduce the risk of lung cancer.