  |
 |
5. What role can diet play in the increased risk of cardiovascular disease in women aged 40 years and over?
Med J Aust 2000; 173 Suppl 6 November: S101-S102 Cardiovascular disease is uncommon in premenopausal women, but thereafter its incidence increases exponentially with age and it is the leading cause of death among women in First World countries. Epidemiological data suggest that dietary factors may influence this risk. Although the association of plasma cholesterol concentrations with risk of coronary heart disease (CHD) is unquestioned, the absolute rates of CHD between populations with similar mean cholesterol concentrations can vary greatly, and may relate to factors including saturated fat content, antioxidant content and non-dietary factors such as cigarette smoking. Among middle-aged women without known vascular disease, adherence to healthy diet, avoidance of smoking and obesity, exercise for half an hour a day, and moderate alcohol consumption were associated with a risk of CHD of less than half that of age-matched women without these lifestyle characteristics.1 Importantly, favourable effects of lifestyle were still evident after adjustment for known risk factors such as age, family history, hypertension, hypercholesterolaemia and menopausal status. In recent years, attempts have been made to isolate the lifestyle and specific dietary factors that may influence this risk. Antioxidants Populations with low rates of CHD consume diets rich in antioxidants such as vitamin E. Further, elevated plasma levels of some antioxidant vitamins are correlated with lower rates of CHD. Some observational studies have shown a relationship between lower rates of CHD and high intakes of vitamin E supplements, but others have shown a protective effect only when vitamin E is consumed as food, and not when it is taken as a supplement.2 This apparent difference between dietary vitamin E and vitamin E supplements may indicate that a high intake of dietary vitamin E is an indirect marker of consumption of nutritious whole foods rather than a simple measure of antioxidant intake. The Iowa Women's Health Study showed an inverse association of wholegrain intake with risk of death from CHD.3 In that study, women who reported eating at least one serving of wholegrain foods a day had a substantially lower risk of mortality from CHD compared with women who reported eating no wholegrain products. The study found that the risk of death from coronary heart disease among women in the highest category of wholegrain intake (median, three serves a day) was only 70% that of women in the lowest category (median, 0.2 serves a day).3,4 Southern European diets containing large quantities of antioxidants also contain large quantities of olive oil, fruits and vegetables, fibre, red wine and garlic, and relatively low levels of saturated fat. Randomly allocating patients to an entire Mediterranean diet (including increased intake of fibre, omega-3 polyunsaturated fatty acids, fruit and vegetables) dramatically reduced CHD recurrence.5 By contrast, supplements of vitamin E, beta-carotene, and retinoic acid have not consistently reduced cardiovascular event rates, despite promising results of studies with surrogate endpoints of vascular disease, such as vessel intima media thickness and endothelial reactivity. In recent placebo-controlled studies, beta-carotene and retinoic acid have been shown to exert no effect on, or even to increase, the risk of lung cancer.6,7 The largest and most recent randomised study of high dose (400IU) vitamin E, a dose well in excess of that consumed in typical Mediterranean diets, failed to show benefit of vitamin E.8 Phytoestrogens Diets rich in phytoestrogens may reduce cardiovascular disease. Specifically, a high intake of soy products is associated with a lower incidence of cardiovascular disease, and the ingestion of vegetable protein, particularly soy, is associated with a reduced risk of CHD and improved risk factor status.9,10 Interventional studies indicate that soy has favourable effects on lipid profiles in primates, including humans, and on blood pressure in humans.11,12 A meta-analysis of controlled clinical trials in humans noted that consumption of soy protein significantly reduced concentrations of total cholesterol (9.3% [-0.6mmol/L] decrease; 95% CI, 0.35-0.85mmol/L), low-density lipoprotein cholesterol (12.9% [-0.5mmol/L] decrease; 95% CI, 0.30-0.82mmol/L) and triglycerides (10.5% [-0.15mmol/L] decrease; 95% CI, 0.003-0.29mmol/L), with little change in high-density lipoprotein concentration.11 Responses were related to patients' pretreatment plasma cholesterol levels. While most research has focused on phytoestrogen-rich whole foods or protein isolates, with little information on concentrated phytoestrogen subfractions in tablet form, the limited data suggest that isolated phytoestrogens are less effective at reducing cardiovascular risk factors.13 Further, soy supplementation has been associated with reduced atherosclerosis in animals and improved vascular function in female monkeys, but not in humans.10,12 The active components of soy are not yet known; potential contributors include vegetable protein, antioxidants and phytoestrogens.9 Homocysteine Elevated levels of homocysteine, an amino acid central to folate metabolism, are considered a risk factor for cardiovascular disease, especially in postmenopasual women.14 However, it is not known whether specific intervention with folate, B-vitamins or dietary modifications will lower homocysteine levels and, in turn, alter cardiovascular risk. Large randomised trials currently under way should clarify this.14
References
Readers may print a single copy of these pages for personal use. No further
reproduction or distribution of the articles
should proceed without the permission of the publisher. For
permission, contact the
Australasian Medical Publishing Company
<URL: http://www.mja.com.au/>
© 2000 Medical Journal of Australia.
|
