We give blood to save someone elses life. It turns out that this altruistic act could also improve the donors health. But they might have to give a lot of blood over time for that effect.A study screened 217 male volunteer blood downers. The researchers divided the group into two. One cohort had given blood over a hundred times during their lifetimes. The other group had done so less than five times.Although the study was initiated in part to investigate whether long-term donation had any negative effects on the donors blood cells, they discovered an unexpected positive effect. Although both groups showed a good diversity of blood cell types, the frequent donors demonstrated some key differences, according to a study in the journal Blood.The Benefits of Giving BloodOne of the most dramatic? Both groups possessed some blood cells with changes to a gene associated with leukemia. But the changes to that gene called DNMT3A were not in the areas associated with preleukemia.To see if this difference was merely an interesting association or a legitimate sign of protection against blood cancer, researchers at the Francis Crick Institute edited DNMT3A from the human stem cells in the lab into two versions. One version contained the genetic changes associated with leukemia and the other matched the preleukemic changes to the gene in the frequent donor group, and also the non-preleukemic changes observed in the frequent donor group.Putting Blood to the TestNext, they grew these cells in two environments. One contained a hormone that stimulates red blood cell production. That hormone, erythropoietin (EPO) is boosted after each blood donation. The other growth environment contained inflammatory chemicals meant to mimic an infection.The cells with DNMT3A mutations seen in the frequent donors grew in the EPO environment and languished in the inflammatory one. The cells with the preleukemic DNMT3A mutations showed the opposite effect.To see if these effects insisted beyond petri dishes, the team transplanted cells with the two different DNMT3A into mice. The scientists mimicked the stress of blood donation in some mice by removing blood and giving them EPO injections.Those blood donor proxy mice exhibited normal red blood cell production, without the cells becoming cancerous. In sharp contrast, mice with preleukemic mutations showed a sharp increase in white blood cells in both control and stress conditions.Our work is a fascinating example of how our genes interact with the environment and as we age," Dominique Bonnet, a Crick scientist and an author of the paper, said in a press release. Activities that put low levels of stress on blood cell production allow our blood stem cells to renew and we think this favors mutations that further promote stem cell growth rather than disease."An All-Clear for DonorsThe study also should come as a relief to frequent blood donors and not just because they may be less at risk for blood cancers. It demonstrates how blood cells adapt to stressors and that many of those adaptations can be positive.Blood donations save lives and even at the deepest molecular level, we see no evidence of an increased risk for donors, Andreas Trumpp a DKFZ researcher and author of the study, said in a press release. Our result now confirms decades of clinical observation with molecular data.Article SourcesOur writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.