Blood pressure may be affected by dietary iron intake, according to a recent study conducted by Ioanna Tzoulaki at the Department of Epidemiology and Public Health, Imperial College London, and colleagues, published in the latest issue of British Medical Journal.

Dietary influences on blood pressure, with sodium, alcohol, caloric imbalance (direct), potassium (inverse), and favorable effects of minerals, vegetable protein, and omega-3 polyunsaturated fatty acids have been previously determined. Now, according to the current study, nonheme iron has been found to reduce blood pressure, whereas heme iron from red meat, one of its main sources, has been found to have an adverse effect on blood pressure.

The study, termed the International Collaborative Study on Macro-/micronutrients and Blood Pressure (INTERMAP), involved 17 population samples from Japan, China, UK and US, which included 2359 were men and 2321 women, all aged between 40 to 59 years. Information regarding the diet was obtained by a 24 hour recall method during each visit, and the average of 8 blood pressure readings was taken as the main outcome measure. After adjusting for various confounding factors, the study observed 1.39 mmHg (P<0.01) lower systolic BP with dietary total iron intake higher by 4.20 mg/4.2 MJ (2 SD), and 1.45 mmHg (P<0.001) lower systolic blood pressure linked to dietary nonheme iron intake higher by 4.13 mg/4.2 MJ (2 SD). However, red meat intake 102.6 g/24 h (2 SD) was associated with 1.25 mmHg higher systolic blood pressure.

In another study, Belfort MB, et al. (Internal Journal of Epidemiology, 2008) sought to determine the relationship between the maternal iron intake and status, and blood pressure of the child at 3 years of age. The study involved 1167 subjects, consisting of a cohort of pregnant women and their children. Maternal iron intake during the first and second trimester was determined by food questionnaires and the children’s blood pressure was measured about 5 times. The maternal hemoglobin and MCV was also recorded during pregnancy. The study found that for every 10 mg increase in first trimester iron consumption, the child’s BP was higher (and not lower) by 0.4 mmHg. It was therefore concluded that there is no association between maternal iron status and blood pressure of offspring at 3 years of age.

Iron plays a vital role in oxygen delivery to body tissues, and hence a deficiency leads to fatigue and decreased work performance. It is consumed in two forms – heme and nonheme. Heme iron is obtained mainly from animal sources such as fish, poultry and red meat, whereas plant sources provide nonheme iron. The former is absorbed more efficiently than nonheme iron and comprises the major portion of the total iron intake in the Western diet. The relationship between iron intake and cardiac disease has been extensively studied, with some trials showing a positive association and others yielding inconclusive results. However, this is one of the first studies focusing on the effect of iron intake on blood pressure, and larger studies in other populations are required before a definite conclusion can be elicited.

References

1. Tzoulaki I, Brown IJ, Chan Q, et al. Relation of iron and red meat intake to blood pressure: cross sectional epidemiological study. BMJ. 2008 Jul 15;337:a258.

2. Belfort MB, Rifas-Shiman SL, Rich-Edwards JW, Kleinman KP, Oken E, Gillman MW. Maternal iron intake and iron status during pregnancy and child blood pressure at age 3 years. Int J Epidemiol. 2008 Apr;37(2):301-8. Epub 2008 Feb 8.

3. Dietary Supplement Fact Sheet: Iron. Office of the Dietary Supplements. Last accessed Jul 26, 2008