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HRT increases risk and severity of stroke

NOTTINGHAM, UNITED KINGDOM. It is widely believed that estrogen is a protective agent that may reduce stroke risk. This is thought to explain the relatively low risk of stroke in premenopausal women which rapidly increases following menopause. Hormone replacement therapy (HRT) supplies the body with synthetic or artificial estrogen alone or estrogen and progesterone combined with the aim of reducing menopausal symptoms and bone loss. Early studies suggested that women on HRT have less heart and blood vessel disease, but these studies were observational and open to bias. On the other hand, some trials have indicated that there is a possible link between HRT and an increased risk of stroke.

Researchers at the University of Nottingham reviewed the results of 28 reliable HRT trials including a total of 39,769 participants. Using a well-established analysis tool they found HRT to be associated with a 29 per cent increase in overall risk of stroke. This increased risk was particularly strong for ischemic stroke, in which part of the brain does not get sufficient blood for a period of time. Stroke severity was also greater in women on HRT, who were 56 per cent more likely to have a stroke leading to death or disability. HRT did not significantly increase the risk of hemorrhagic stroke (caused by bleeding in the brain) or transient ischemic attack ('mini-stroke'), but in none of the studies did HRT reduce stroke risk.

The authors report that it remains unclear why HRT should increase rates of ischemic stroke and its severity. They speculated that progesterone might be the likely cause, since progestogens can promote atherogenesis and vasoconstriction (restriction of the blood flow in blood vessels), but further analysis of the studies did not support this theory. Given these findings, HRT cannot be recommended for the primary or secondary prevention of stroke, and it may not be safe for women at high risk of stroke, they conclude.
Bath, P M W and Gray, L J. Association between hormone replacement therapy and subsequent stroke: a meta- analysis. British Medical Journal, Vol. 330, February 2005, pp. 342-345

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