An eight-year prospective study of more than 30,000 postmenopausal Swedish women found that those who were using or had used HRT had significantly higher rates of cataract removal, compared with women who had never used HRT. Alcohol consumption seemed to increase HRT's harmful effect. The HRT study was led by Birgitta E. Lindblad, MD, Sundsvall Hospital, Sweden as part of the Swedish Mammography Cohort (SMC), established to study lifestyle factors and chronic diseases.
"If future studies confirm the associations we found, increased risk for cataract removal should be added to the list of potential negative HRT outcomes," Dr. Lindblad said.
More than 4,300 cataract removal surgeries were performed in participants between 1997 and 2005. The risk for cataract removal was increased by 14 percent in women who had ever used HRT and by 18 percent in current HRT users, compared with women who never used HRT. Longer duration of HRT use correlated with increased risk. Current HRT users who also reported having more than one alcoholic drink per day had 42 percent increased risk compared with women who used neither HRT nor alcohol. Smoking status did not significantly affect risk. Data were adjusted for exposure to external (exogenous) estrogens such as birth control pills, as well as reproductive and other health factors.
"Cataract is more prevalent in postmenopausal women than in men at similar ages; this implies that hormonal differences are involved and suggests a possible role for estrogen," Dr. Lindblad explained. She described how HRT may act to promote cataracts and also compared her project's findings with earlier studies.
Estrogen receptors have been detected in the eye's lens, the area that becomes cloudy and inflexible when a cataract develops. Naturally occurring (endogenous) estrogen appears to protect the eye from cataract, along with guarding cardiovascular and other body systems before menopause. Exogenous estrogens like those used in HRT do not function the same way. For example, HRT increases C-reactive protein levels, associated with cataract development in other studies. Dr. Lindblad's study also describes how alcohol and HRT may interact to raise estradiol levels, which appears to affect cataract risk.
In contrast to the SMC, earlier large HRT and cataract risk studies in the United States, Australia and Europe reported mixed results; importantly, some of these studies included women who were premenopausal and so possibly protected by endogenous estrogen. Results of the Swedish study may have been impacted by factors unique to this population: for example, nearly all participating women shared the same ethnicity, and all had equal access to care. The study did not identify type of HRT, type of cataract, or measure exposure to excess sunlight (a risk factor for cataract, although unlikely to impact residents of northern Europe).
This research is reported in the March issue of Ophthalmology, the journal of the American Academy of Ophthalmology.
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