*The role of this risk factor in the development of heart disease is not yet fully established. While it has been shown to be associated with heart disease and heart attacks in some studies, other studies have not found a similar association. In addition, it has not yet been shown that altering iron levels will lower your risk for heart attack or dying early.
What is the Iron Hypothesis?
The “iron hypothesis” states that the reason premenopausal women have lower rates of heart disease than postmenopausal women and men is because they have less iron stored in their bodies. Premenopausal women have less iron because of the blood shed during their period—blood is a primary storehouse for iron.1 When the regular blood loss stops at menopause (when you no longer get your period), your iron levels gradually rise. Some researchers hypothesize that this increase in iron levels may, in part, explain the increased risk of heart disease after menopause.
The conventional wisdom is that the relatively low rates of heart disease in premenopausal women are due to the heart-protecting effects of the female hormone estrogen. However, the iron hypothesis received more attention after large studies found that hormone therapy did not lower the risk of heart disease in postmenopausal women. Currently, there isn't enough evidence to prove or disprove the iron hypothesis. Some studies have shown that people with high iron levels are more likely to have a heart attack,2 but others have found that iron levels don't predict a person's risk for heart disease, nor do they tell you anything about how severe your heart disease may be.3
Why does the body need iron?
Iron forms part of a number of essential proteins in the body, perhaps the most important of which is hemoglobin. Hemoglobin is the part of red blood cells that carries oxygen throughout the body. Without iron, red blood cells can't bind properly to the oxygen molecules. Approximately two thirds of iron in the body is found in hemoglobin. The iron gives our blood its deep red color. The rest of the iron is stored in various places, such as the muscles and inside cells.3 It is also an essential part of the immune system and energy production.
Where does my body get iron?
Our bodies get iron from the food we eat. Iron in the diet comes in two forms: heme iron from animal foods (e.g., red meat, fish and poultry) and non-heme iron from mostly plant foods (such as broccoli, spinach, and almonds); over-the-counter vitamin supplements; and iron-fortified or iron-enriched foods (such as breakfast cereals). You absorb about 15% to 35% of the heme iron that you eat. The amount of iron that your body absorbs varies depending on whether your iron levels are low or high. If your iron levels are low, your body will absorb more iron from the food you eat to make up the difference. If levels are high, your body will absorb less iron from your diet. In general, non-heme iron is not as easy for the body to absorb as heme iron. However, once the iron is absorbed, your body no longer distinguishes between the sources of this mineral (heme vs. non-heme).
Other foods or drinks in your diet can affect the amount of non-heme iron that you absorb (heme iron isn't affected in this way). Meat proteins, alcohol, and vitamin C increase the amount of non-heme iron that you absorb whereas caffeine, tannins (found in tea), calcium, polyphenols (found in wine and dark, unprocessed chocolate), and phytates (found in legumes and whole grains) decrease the amount of non-heme iron you absorb.4 For example, if you eat beans or dark leafy greens with some lean meat, fish, or poultry, you will absorb up to 3 times more non-heme iron than if you ate the meat or fish by itself.5
What other factors affect iron levels?
The main way that women lose iron is through their menstrual period. Contraceptive methods that affect menstrual blood loss also affect iron loss in women: bleeding is higher with certain intrauterine devices and lower in women taking oral contraceptives. After menopause, the iron levels in a woman's body increase. Taking hormone therapy may reduce this effect, partly because of hormone-induced bleeding.6