The most red-blooded of essential minerals has a dark side, and it’s mainly because of the meat
By SYD BAUMEL
Iron, that most red-blooded of essential nutrients, has a dark side.
>And it’s not just people with the uncommon genetic condition of hemochromatosis – which causes a life-threateningly toxic buildup of iron in the body – who have reason to fear it.
Studies suggest a modest iron overload from diet alone can do serious damage to any one of us, increasing our risk for heart disease, type 2 diabetes and even, perhaps, cancer and Alzheimer’s disease.
For decades, scientists have been trying to get to the bottom of the problem – assuming there even is one (the jury is still out).
Lately, the evidence has mounted that it’s not just any iron that may harm us. Increasingly, the finger of suspicion is pointing exclusively at heme iron, the extremely bioavailable form found only in animal foods, especially red meat, liver and seafood.
Unlike non-heme iron (the only kind found in plant foods), heme iron is a complex organic molecule that is very readily absorbed by the intestines and held onto so strongly by our bodies that we have a hard time losing it, even if we’ve accumulated too much already.
Bleeding is about the only way we can get rid of it.
Back in 1981, a pathologist named Jerome Sullivan hypothesized that this sticky property of iron is responsible for the relatively low heart disease rate among premenopausal women who, every month, lose lots of blood loaded with heme iron-rich hemoglobin. In contrast, iron simply accumulates in men’s bodies as they age – at least on the proverbial steak and potatoes diet. It’s the same for women after menopause, which is when they become equal opportunity heart disease candidates..
It wasn’t just the coincidentalness of all this that aroused Sullivan’s suspicions. Iron fits the dangerous offender profile. Among all the good things it does in the body (which is why it’s an essential nutrient), iron is an oxidant, as in the opposite of antioxidant. Given the opportunity, it’s more than happy to damage (oxidize) fragile biochemicals like cholesterol and cellular fatty acids in ways that put us at greater risk for heart disease and other illnesses.
Three decades and scores of long-term studies since Sullivan first published his “iron hypothesis” in The Lancet, the cumulative evidence suggests he was more likely right than wrong, according to two independent meta-analyses of the observational studies published last year.
In one, based on nearly 300,000 people followed for an average period of over 10 years, folks who had consumed the most heme iron had a 57 percent greater risk of developing coronary heart disease (CHD) than those who consumed the least. (In studies like these, “most” and “least” typically compares people in the top and bottom 20th, 25th or 33rd percentile of intake.) Their risk of dying from CHD was nearly 40% higher, although this difference wasn’t statistically significant. In contrast, high consumers of non-heme iron – which the body absorbs as poorly as it lets go of easily – had, if anything, a moderately lower CHD risk.
In the other meta-analysis, the CHD risk from consuming high amounts of heme-iron was somewhat lower, but the authors went so far as to morbidly calculate a “dose-response.” For each milligram of heme iron in a person’s daily diet, their long-term risk for CHD rose by 27% (between 10% and 47% with a 95% statistical probability). In a companion study published this year, the same team looked at heme iron and all forms of cardiovascular disease (CVD) combined: CHD and heart attacks, strokes, high blood pressure, heart failure, arrhythmias and more. This time the dose-response was a little more forgiving: a 7% increased risk of CVD for every milligram of heme iron.
Non-heme iron? Zero risk.
To consume a milligram of heme iron, you only need to eat about an ounce of liver or seafood, one and a half ounces of beef, turkey or canned sardines or four ounces of chicken, pork or fresh fish.
It makes you wonder if heme iron could help explain why vegans and vegetarians are much less prone to cardiovascular disease – and type 2 diabetes and colorectal cancer (read on). (Note: The cardio benefit is likely clawed back in vegans who don’t get enough vitamin B12 from supplements or fortified foods. Low B12 promotes CVD.)
Several observational studies have also implicated iron overload as a risk factor for type 2 diabetes, and once again the finger is pointing at heme iron. As health columnist Jane Brody writes in the New York Times: “… among 32,000 women followed for 10 years in the Nurses’ Health Study, those with the highest levels of stored iron were nearly three times as likely to have diabetes as those with the lowest levels. Likewise, among 38,000 men in the Health Professionals Follow-up Study, those who consumed the most heme iron had a 63 percent greater risk of developing diabetes.” Brody is referring to two flagship studies from the Harvard School of Public Health. The same pattern has been observed in other long-term studies from the United States, China and Spain.
As one moves beyond CHD and diabetes, the evidence against excess iron (heme or otherwise) gets more tenuous. Too much of it may or may not increase one’s risk for colorectal cancer (or it may be due to other culprits in red meat) and for the neurodegenerative bogeymen, Parkinson’s disease and Alzheimer’s (or the diseases themselves may let destructive amounts of iron leak into the brain).
If there’s a precautionary message, perhaps it’s that non-heme iron – which is the only kind we ever get from plant foods – is a take-it-or-leave-it proposition for our bodies. When we’re short of iron, our bodies step up and absorb it more readily. If we already have lots, they absorb it even less than usual. Not so for heme iron, which is always absorbed very efficiently – and retained – even if we already have too much.