If you take a multivitamin supplement or a heavily fortified cereal (such as Product 19 or Total), be sure to check the label for the amount of iron it contains. A multivitamin supplement that contains 18 mg of iron (or a cereal that contains 100% of the daily value for iron, which is also 18 mg), for example, is fine for most women under 50. However, this is too much iron for men and postmenopausal women, who should choose a supplement with no more than 8 or 9 mg of iron. In fact, men, postmenopausal women, and anyone who is at risk for iron overload can switch to a multivitamin that contains no iron, such as One-A-Day Men’s High Potency Multivitamin/Multimineral Supplement.
As mentioned earlier, iron overload, in which excess iron is in the blood and becomes stored in vital organs, such as the liver and heart, can be caused by getting too much iron from a supplement. A common genetic condition called hemochromatosis can also cause the body to absorb too much iron. Over time, iron builds up in organs, leading to problems such as cirrhosis (damage to the liver) and heart failure. Although some studies have found no connection, others have found a link between hemochromatosis and diabetes. Hemochromatosis occurs in about 1 out of 250 people of Northern European descent and is less common in other ethnic groups. This condition is often not diagnosed until signs of organ damage occur, which is another reason why men and postmenopausal women who are not iron-deficient should not take iron supplements unless prescribed by their health-care provider.
Iron and bone health
New research shows that iron may be just as important as calcium and vitamin D in building and maintaining healthy bones. A study published in the November 2003 issue of the Journal of Nutrition looked at the effect of iron on bone mineral density in 242 postmenopausal women. Women who consumed approximately 20 mg of iron, along with an intake of 800–1200 mg of calcium per day, had the greatest bone mineral density. This study illustrates an interesting paradox because calcium reduces iron absorption. Of course, other nutrients are essential for bone health, too, such as vitamin K and phosphorus.
Iron and Type 2 diabetes
Two recently published studies have established a link between high iron levels and the development of Type 2 diabetes. One study, out of the Harvard School of Public Health, looked at data gathered from approximately 33,000 healthy women (none of whom had diabetes) participating in the ongoing Nurses’ Health Study. After 10 years of follow-up, about 700 of these women developed Type 2 diabetes. These 700 women also had significantly higher iron stores (shown by high levels of the iron-storing molecule ferritin) compared to a control group of about 700 women who did not develop diabetes. Women with the highest ferritin levels were almost three times as likely to develop diabetes than women with low ferritin levels. Although a single study isn’t conclusive, the thought is that high iron levels in the blood may increase the formation of free radicals (highly reactive by-products of normal chemical reactions in the body), causing insulin resistance and impaired glucose metabolism.
The other study used data from the Iowa Women’s Health Study, which followed about 36,000 postmenopausal women without diabetes for 11 years. Women who drank alcohol and had a greater intake of iron (from iron supplements or heme iron from meats) had an increased risk of Type 2 diabetes compared to women who did not drink alcohol. The researchers also discovered that among women who did not drink, more nonheme iron in the diet corresponded to decreased risks of developing diabetes.
The link between iron and Type 2 diabetes may apply to men as well. Researchers from the Harvard School of Public Health published a study earlier this year in the American Journal of Clinical Nutrition. They looked at iron intake and blood donation data in about 33,000 men without diabetes who participated in the Health Professionals’ Follow-up Study. Men whose iron intake came primarily from red meat were at higher risk for Type 2 diabetes compared to men who got their iron from nonred meat or nonmeat sources. Blood donations were not linked with Type 2 diabetes.