Etiology of common acquired melanocytic nevi: constitutional variables, sun exposure, and diet.

Associations were sought between prevalence of nevi on the arms and other variables in controls from a case-control study of cutaneous malignant melanoma. The prevalence of nevi was higher in women than men, fell with age up to about 35 years of age, and was low in those born outside Australia. Among pigmentary characteristics, there was strong evidence only of an association with skin color of the upper inner arm. The highest prevalence of nevi was in those with skin of intermediate darkness. Peak prevalence of nevi was also seen in intermediate categories of variables indicating sun exposure, particularly mean annual hours of bright sunlight at places of residence when 10-24 years of age, total outdoor exposure time per week in the summer at 10-24 years of age, and usual summer suntan on the arms in the last 10 years. These dose-effect patterns may indicate conflicting effects of sun exposure on appearance and disappearance of nevi. The protective effect of birthplace outside Australia appeared to be due to the corresponding low mean annual hours of bright sunlight at places of residence when 10-24 years of age. The prevalence of nevi was comparatively lower in those who drank alcohol and in those who had average or high daily intakes of retinol. These associations were not explained by those of any of the other variables.