Frequent blood donation does not have any long-term health risks especially of cancer.
There are several unproven theories by which frequent blood donation could affect health. For one, drawing blood causes the body to increase production of blood cells in the bone marrow. This accelerated cell division, or "mitotic stress," could theoretically increase the likelihood of cancer of the bone marrow. Giving blood has also been shown to result in immune system changes, and some have suggested these immunologic effects could be associated with cancer.
To better understand how repeated blood donations affect health, Swedish and Danish researchers evaluated the records of 1,110,212 individuals who donated blood at least once between 1968 and 2002. No relationship was found between how frequently a person gave blood and their risk of cancer. However, among male donors, the risk of liver, lung, colon, stomach and throat cancer declined as the frequency of donations increased, which suggests that iron depletion may reduce cancer risk. It was also found that there was an increased risk of non-Hodgkin’s lymphoma among frequent plasma donors, but this was only seen among people who donated plasma before 1986, but this finding needs careful interpretation.
The findings suggest that there is no risk of cancer associated with frequent blood donation. On the positive side, excess iron stores have been linked to heart disease and certain types of cancer, so people who have their blood drawn regularly may be lowering their risk of cancer.
Journal of the National Cancer Institute,