From Cancerhelp UK:

"...Another study called the �Beta Carotene and Retinol Efficacy Trial�(CARET), looked at whether beta carotene and retinol (vitamin A) could prevent cancer in men and women smokers and ex smokers. The people in the trial were aged from 45 to 69. This trial was also randomised and some participants took a placebo pill. After an average of 4 years of taking the pills, there were 28% more cases of lung cancer diagnosed in people taking the supplements. But 6 years after stopping the pills, the risk of lung cancer had decreased and was almost the same as for people who had not taken the supplements."

As with prescription drugs, it's best to take a look at the contraindications before taking them...and get tested for deficiencies before adding fat-soluable vitamins A, D and E.

Fat soluable vitamins are stored by the body, large doses are toxic. Excess water soluable vitamins, such as C, the B's, etc. get excreted.

Also, some vitamins and minerals are more effective if taken at separate times...such as iron and zinc. Beta Carotene combined with vitamins E, C and Selenium can act together to reduce good serum cholesterol counteracting the benefit of Niacin which increases good cholesterol. That same combination of supplements should not be used by people who are taking statins for cholesterol management.

BTW...There is research data that says that men should not take iron unless it is determined there is a deficiency/anemia. Excess dietary iron from animal-based sources can lead to heart valve damage and heart disease. Curiously, iron from plant-based sources is excreted when there is sufficient stored iron. But, dietary iron from animal-based sources is stored by the body despite there being a sufficient amount of iron stored