Scientific Update

A large British study, with more than 2000 male and close to 9000 female participants, examined the risk of hypertension in meat eaters, fish eaters, vegetarians, and vegans. People with hypertension are at increased risk for both heart disease and stroke. Meat eaters were most likely to report that they had been diagnosed with hypertension (15% of men and 12% of women studied). Vegans were least likely to report being diagnosed with hypertension (close to 6% of men and 8% of women). Self-reported hypertension in fish eaters and vegetarians was between that of meat eaters and vegans. However, there was no significant difference in its occurrence between fish eaters and vegetarians.

In addition to examining whether people had been told they had hypertension, this study also measured blood pressures of the four groups. Meat eaters had the highest measured blood pressure, while vegans had the lowest values. Again, fish eaters and vegetarians had similar blood pressures that were between those of meat eaters and vegans. The main explanation for the differences between the groups was that non-meat eaters, especially vegans, were leaner. The results of this study suggest that a vegan diet may reduce risk of hypertension and that it is not necessary to eat fish to control blood pressure. (This has been recommended by some groups.) Vegans in this study appear to have lower risk of heart disease and stroke due to their lower blood pressure.

Appleby PN, Davey GK, Key TJ. 2002.

Hypertension and blood pressure among meat eaters, fish eaters, vegetarians and vegans in EPIC-Oxford. Public Health Nutr 5:645-54.

Mercury, Fish Oil, and Risk of Heart Disease

Is it necessary to eat fish to reduce risk of heart disease? Although some groups have recommended this, recent studies raise concern about the mercury levels in fish. Fish, especially fatty fish and fish oil, are significant dietary sources of mercury, which may predispose people to heart disease. Two studies examined whether the mercury content of fish counteracts the beneficial effects that the omega-3 fatty acids found in fish have on the heart.

The first study (Guallar) examined close to 700 men throughout Europe and Israel who had had a heart attack. They were compared to almost 700 men who had not had a heart attack. The toenail mercury level in men who had a heart attack was 15% higher than in those who had not. The level of mercury in the men was related to blood levels of DHA, a fatty acid found mainly in fish. This suggests that high levels of mercury were due to higher fish consumption. A beneficial effect of higher blood levels of DHA was not seen unless mercury levels were controlled for. This suggests that the high mercury content of some fish may markedly reduce any beneficial effects of fish oil on risk of heart disease.

The second study (Yoshzawa) was smaller but may have had similar results if only a large number of dentists had not been included. Dentists would be expected to have higher levels of mercury due to their exposure to mercury in their practice. However, this form of mercury is different from the methylmercury found in fish and may have a different effect on the risk of heart disease. These studies suggest that there should be some rethinking of recommendations to eat fish for your heart. (For more information about recommendations related to fish consumption, see Vegetarian Journal Sept/Oct 2001, American Heart Association Calls for Eating Fish Twice Per Week-What's a Vegetarian To Do?)

Guallar E, Sanz-Gallardo I, Van't Veer P, et al. 2002.

Mercury, fish oils, and the risk of myocardial infarction. N Engl J Med 347:1747-54.

Yoshzawa K, Rimm EB, Morris JS, et al. 2002.

Mercury and the risk of coronary heart disease in men. N Engl J Med 347:1755-60.

Calcium Absorption in the Elderly

Calcium recommendations for older people call for a calcium intake of 1200 milligrams daily. While cow's milk is traditionally recommended as a source of calcium, many older people may be lactose intolerant or prefer to avoid dairy products for other reasons. A recent study examined whether calcium could be well absorbed from sources other than cow's milk. Twelve subjects, approximately 70 years old, were given calcium-fortified orange juice, cow's milk, or a calcium supplement containing calcium carbonate. All three forms of calcium appeared to be well-absorbed. We recognize this is a small study; however, it suggests that older people do not need to rely on cow's milk as a good source of calcium-either calcium carbonate supplements or calcium-fortified juice can be used to help meet calcium needs.

Martini L, Wood RJ. 2002.

Relative bioavailability of calcium-rich dietary sources in the elderly. Am J Clin Nutr 76:1345-50.

How Can You Avoid Having Too MUCH Iron?

Iron deficiency is certainly a health problem. Too much stored iron can also be problematic; it has been tentatively associated with heart disease, cancer, and diabetes. Generally, iron stores, as measured by serum ferritin, increase with age until about the sixth decade when they level off. A large study of elderly Americans found that close to 13% had high iron stores, suggesting that iron absorption was not reduced when iron stores were high, as is usually the case. Researchers examined the diets of these individuals to find out if dietary factors or supplement use contributed to the risk of having high stores of iron. They found that those subjects who took more than 30 milligrams daily of iron supplements tended to have high iron stores. Eating more than four servings of red meat per week also increased the risk of having high iron stores, as did eating fewer than seven servings of whole grains per week. Vitamin C, found in fruit, increases iron absorption, so eating more than 21 servings of fruit a week, along with the other previously mentioned factors, also increased risk of elevated iron stores. These findings suggest that older Americans should limit the amount of red meat that they eat, eat more whole grains, and avoid high-dose iron supplements unless prescribed by a health care professional.

Fleming DJ, Tucker KL, Jacques PF, et al. 2002.

Dietary factors associated with the risk of high iron stores in the elderly Framingham Heart Study cohort. Am J Clin Nutr 76:1375-84.

Dietary Guidelines: An Effective Tool for Reducing the Risk of Chronic Disease?

The most recent edition of Dietary Guidelines for Americans was published in 2000 by the USDA and the US Department of Health and Human Services. The Dietary Guidelines consist of 10 recommendations to reduce risk of chronic diseases, such as heart disease, cancer, and diabetes. Several recent studies have examined whether people who adhere to these guidelines really do have a reduced risk of chronic disease. Harnack and co-workers found that adherence to the guidelines specifically related to diet had little effect on cancer incidence; a reduction in cancer incidence was only seen in people who met the guidelines to aim for a healthy weight and be physically active each day. McCullough and other researchers with the American Cancer Society and Harvard University criticize the Dietary Guidelines for promoting dairy and meat intake and calling for an excessively high carbohydrate intake. They call for revising the Dietary Guidelines so that they recommend limiting red and processed meats and promote diets high in fruits, vegetables, and whole grains.

McCullough ML, Stampfer MJ. 2002.

The Dietary Guidelines for Americans and cancer risk in women: still a long way to go. Am J Clin Nutr 76:701-2.

Harnack L, Nicodemus K, Jacobs DR, Jr, Folsom AR. 2002.

An evaluation of the Dietary Guidelines for Americans in relation to cancer occurrence. Am J Clin Nutr 76:889-96.

McCullough ML, Feskanich D, Stampfer MJ, et al. 2002.

Diet quality and major chronic disease risk in men and women: moving toward improved dietary guidance. Am J Clin Nutr 76:1261-71.