Do multiple families alter estimates of risk for age-related cataract in a population-based study? The Beaver Dam Eye Study.

We sought to determine the effect of "genetic" load on the strengths of risk factors for age-related cataracts in the population-based Beaver Dam Eye Study. Of the 4,926 participants in the baseline examination in 1988 to 1990, 2,338 were members of 594 family groups. There were no important differences in the risks due to pack-years smoked, systolic and diastolic blood pressures, body mass index, current smoking, hypertension or hormone replacement therapy for either the whole population or subgroups created by omitting siblings or any family relation. There were some differences when the analyses were limited to only a randomly selected family member or a randomly selected sibling. These latter findings may relate to the older average age of those in sibships or in families compared to those not in families. We conclude that for the associations we explored, the relatively large number of families in our population had little effect on the strengths of the risk factors, and that limiting analyses to only those not in families may distort risk factor associations by altering the age structure in this population.