By Janet R. Hunt
Three years ago in a column similar to this, I wrote of the dual impact of diet and genetics on our health, and solicited volunteers from the local community to participate in a study to determine if a common DNA characteristic (mutation) influences dietary iron absorption. My collaborator, Dr. Huawei Zeng, and I are grateful to 359 local volunteers who helped to determine that the approximately 10% of us that carry a single copy of this DNA mutation need not worry about absorbing too much iron.
More than 80% of the victims of hemochromatosis, an iron storage disorder, carry two copies (one from each parent) of this DNA mutation. People with hemochromatosis accumulate such excessive amounts of iron in their vital organs that they become ill in mid-life, with a high susceptibility to cancer, diabetes, and liver failure, with the risk of an early death. If the excessive iron accumulation is detected before permanent organ damage occurs, the disease can be successfully treated by the regular withdrawal of blood to reduce body iron. The 1996 discovery of the specific DNA mutation associated with this disease held the promise of early identification and treatment of those susceptible.
This genetic mutation is relatively common in people of Northern European origin (one of the geneticists who discovered it speculated that it was a genetic characteristic spread by the Vikings). Although only 0.3% of the white, non-Hispanic U.S. population have inherited the mutation from both parents, nearly 10% have inherited it from one parent. If these 10% absorb iron excessively, U.S. practices of fortifying foods with added iron may need to be modified. With our local Scandinavian heritage, Grand Forks seemed like a good place to investigate this possible interaction between nature and nurture.
In one of the first genotyping studies to be approved by the University of North Dakota, local volunteers gave the USDA Grand Forks Human Nutrition Research Center permission to test their DNA from inside their cheeks or from a blood sample. Despite our Scandinavian heritage, only 7% of the group carried the genetic mutation, but this was probably just random luck, not statistically different from the nearly 10% national average. Iron absorption measurements in a third of these volunteers revealed that iron absorption was greater in those with the lowest body iron stores, but was not different in those carrying a single copy of the genetic mutation associated with hemochromatosis. This suggests that iron fortification of foods does not pose a special health risk to these members of the population.
In the meantime, research by others has revealed that, while most people with the disease have dual copies of the mutation, so do many people with no signs of iron accumulation. Perhaps the latter group has yet-to-be-identified protective genetic, diet, or lifestyle characteristics. It is apparent that there are many factors that affect our overall susceptibility to such diseases. Through research, including the contributions given by research volunteers, we will improve our understanding of diets and lifestyles that can maximize our genetic potential for good health.