The study also found that use of retinol and lutein supplements for four years or longer was associated with increases in lung cancer risk of 53 per cent and 102 per cent, respectively.
This is not the first time that concerns over beta-carotene supplements for smokers have been raised. Indeed, two high profile clinical trials, the Beta-Carotene And Retinol Efficacy Trial (CARET) in the United States and the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) trial in Finland, reported that beta-carotene, alone or in combination with vitamin E or retinyl palmitate, could increase the risk of lung cancer by 36 and 16 per cent, respectively, compared to placebo.
“We wanted to see if the same results [as the clinical trials] would be found if we looked at use of these supplements in the general population,” explained lead author Jessie Satia, PhD.
The study, published in the American Journal of Epidemiology, could not detect a link between beta-carotene and other carotenoids and lung cancer risk among non-smokers.
“This observational epidemiologic study is one of the first to report that long-term use of individual beta-carotene, retinol, and lutein supplements is associated with elevated lung cancer risk, results generally in agreement with randomized clinical trials,” wrote the researchers.
“Although the results do not universally suggest that retinol, beta-carotene, and other carotenoid supplements increase lung cancer risk, there is clearly no evidence of a protective effect.
“These findings are particularly relevant to those who use the individual supplements; they suggest that long-term use of these supplements, at doses higher than in a typical multivitamin, may be harmful with regard to lung cancer risk,” they added.
Satia and her co-workers used questionnaires to assess use of dietary supplements, including multi-vitamins and individual nutrients, by more than 77,000 Americans between the ages of 50 and 76.
The researchers documented 521 cases of lung cancer, and that certain people, especially smokers, were at higher risk of developing lung cancer than the general population if they took supplements containing certain nutrients.
Furthermore, a smokers’ risk of developing lung cancer was found to increase with increasing length of time of supplementation with beta carotene, retinol and lutein.
“The risk increased the longer the person had taken the supplements,” said Satia. “The amount of time the person took supplements seemed to have a greater effect than the dose. Even a modest dose, if taken for a long time, can increase the risks of lung cancer, especially among smokers.”
No risk for non-smokers was calculated since the incidence of lung cancer among these people was small, said Satia.
“We believe beta-carotene is an antioxidant, but it seems that if you take too much, at some point it can have pro-oxidant effects, which can result in elevated cancer risk,” she added.
Lung cancer is the most common form of cancer worldwide with over 1.2m new cases diagnosed annually, according to the European School of Oncology. It has one of the lowest survival rates with only 25 per cent of patients surviving more than one year after diagnosis (England and Wales).
Tomorrow, NutraIngredients will run reaction to this study.
Source: American Journal of EpidemiologyPublished online ahead of print, doi: doi:10.1093/aje/kwn409 “Long-term Use of β-Carotene, Retinol, Lycopene, and Lutein Supplements and Lung Cancer Risk: Results From the VITamins And Lifestyle (VITAL) Study” Authors: J.A. Satia, A. Littman, C.G. Slatore, J.A. Galanko, E. White