Risk factors for age-related cataract : a prospective cohort study

Abstract

Cataract is the most common cause of blindness in the world. Epidemiologic studies have shown that the etiology of cataract is multifactorial. Cataract increases with age and oxidative damage to the lens proteins is suggested to be of importance. The only currently available treatment is surgical extraction of the lens; two thirds of these operations are performed in women. Today in Sweden cataract extraction is the most common operation, with nearly 80,000 operations being performed each year among a population of 9 million inhabitants. The number of cataract extractions has increased dramatically during the last two decades due to improvements in the operation technique leading to earlier intervention, and an increasing elderly population.

Cataract involves decreased vision and deteriorated quality of life resulting in socio-economic consequences. Elderly individuals with compromised vision require assistance. Furthermore, expenses increase due to a rise in operation volumes. Therefore, finding modifiable risk factors for cataract is of public health importance.

Cigarette smoking, UV-exposure, diabetes and steroid medication have been associated with cataract in previous studies. Alcohol consumption, abdominal adiposity, hypertension and postmenopausal hormone therapy may be associated with cataract development. Dietary patterns and vitamin supplement use could also be of importance.

The aim of this thesis was to investigate the association between smoking intensity; smoking cessation; alcohol consumption; metabolic syndrome with its components of abdominal adiposity, diabetes and hypertension; and postmenopausal hormone therapy, with the incidence of age-related cataract extraction among women in the Swedish Mammography Cohort (SMC). About 35,000 women in the cohort (born 1914-48) and living in Västmanland and Uppsala county, filled in a mailed questionnaire on diet, height, weight and lifestyle factors in 1997. During the study period, September 1997 until October 2005, a total of 4,508 incident cases of age-related cataract extraction were identified by linking the study cohort, using personal identification number, with computerized registers of cataract extraction in the two counties.

Cox proportional hazards models were used to estimate relative risk as rate ratio (RR) with 95% confidence interval (CI) adjusted for potential confounders.

Smoking was associated with a 17 % increased risk of cataract extraction with a significant dose-response for intensity of smoking , measured as the average number of cigarettes smoked per day during smoking life-time. Quitting smoking predicted reduced risk over time, but a longer time was needed for those with a higher smoking intensity.

Alcohol consumption was associated with a modest (10%) increased risk of cataract extraction. The risk increased with increasing alcohol consumption. An increment of alcohol consumption with 1 alcoholic drink per day (equivalent to 13 gram alcohol per day), was associated with a 7% increased risk of cataract extraction. Women who smoked as well as used alcohol had cataract extractions five years earlier than women who did neither.

Abdominal adiposity (waist circumference >= 80 cm), diabetes and hypertension were positively associated with risk of cataract extraction, the observed risk being 8 %, 43 % and 12 % respectively. Women with all three component of the metabolic syndrome had an even greater risk (68%); those younger than 65 years of age had an almost 3 fold increased risk of cataract extraction associated with the metabolic syndrome.

Current use of hormone replacement therapy (HRT) among postmenopausal women was associated with an 18% increased risk for cataract extraction. The risk increased with duration of HRT use. Current users of HRT consuming more than one alcoholic drink per day had an even higher risk (42%) for cataract extraction.

In conclusion, healthy life-style promotions like smoking prevention or cessation, modest alcohol consumption, and weight control, as well as a restrictive use of HRT, could delay the development of cataract.