What these researchers always fail to do is to use all of the vitamin A complex. The fact is that a very large percentage of the population CANNOT convert beta-carotene to vitamin A. And that's the rub.
Back to the drawing board boys. Give real vitamin A (best from cod liver oil) along with the other fractions you tested (and were they synthetitic vitamins?) and see what a different outcome you'll achieve.
Carotenoid supplements tied to lung cancer risk
NEW YORK (Reuters Health) – Based on the findings from a new study, it appears that people who take higher than recommended doses of carotenoid supplements hoping to keep from getting sick, may actually be doing themselves harm. The long-term use of beta-carotene, retinol, and lutein supplements at doses higher than in multivitamins, increases lung cancer risk, especially in smokers and former smokers, according to investigators from the Vitamins and Lifestyle (VITAL) study.
High-dose beta-carotene supplements increase the lung cancer rates in high-risk individuals, even though carotenoids from dietary sources tend to lower risk, Dr. Jessie A. Satia and co-researchers note in the American Journal of Epidemiology. "Whether effects are similar in the general population is unclear."
Satia's team analyzed data from 77,126 subjects ages 50 to 76 who filled out questionnaires in 2000-2002 regarding supplement use over the previous decade. The group was predominantly white and generally healthy, the authors note, and while there were few who never smoked among the lung cancer cases, there were fewer current smokers in the overall group than in the general population.
By linking the data to the national cancer registry, Satia, at the University of North Carolina at Chapel Hill, and her colleagues identified 521 cases of lung cancer. They then estimated the risk associated with the individual supplements after considering the possible effects of age, gender and smoking history.
Each supplement raised the risk of non-small-cell lung cancer, the most common type of lung cancer, with retinol and lutein also having a modest association with lung cancer overall.
When beta-carotene was used for at least 4 years, the overall risk of lung cancer was not significantly increased, but the risk of small-cell lung cancer rose by more than 3-fold.
For retinol, the overall risk of lung cancer increased by more that 50 percent and for non-small-cell lung cancer, it increased by 80 percent.
For lutein, the overall risk increased by 2-fold, while the corresponding risk for non-small-cell lung cancer increased by 2.5-fold.
The researchers speculate that "these nutrients from supplements may be more bioavailable than those from dietary sources" and large amounts of these supplements might interfere with the absorption, transport and or metabolism of micronutrients or other carotenoids that may be protective against lung cancer.
"Too high a dose of an antioxidant vitamin may interfere with generation of reactive oxygen species needed for beneficial processes, such as normal immune response and apoptosis," Satia's team adds.
Whatever the reason, they conclude that the "long-term use of individual beta-carotene, retinol, and lutein supplements should not be recommended for lung cancer prevention, particularly among smokers."
SOURCE: American Journal of Epidemiology, April 1, 2009.
Copyright © 2009 Reuters Limited.