MAY 13, 2011
A recent nation-wide study found a strong protective association between vitamin D status and the prevalence of early AMD. This study was conducted to see if those results would hold true in a second study, the Carotenoids in Age-related Eye Disease Study (CAREDS), in which 25-hydroxyvitamin D concentrations were assessed six years prior to AMD status.
Data from CAREDS also allowed investigator to adjust for the major non-genetic risk factors for AMD as well as explore relationships between other surrogate measures for vitamin D status, such as oral sources of vitamin D and sun exposure. Subjects in the CAREDS study were 1,313 women aged 50 to 79. Overall, 241 women developed early AMD and 26 developed advanced disease. The median serum 25 (OH)D level was 30 nmol/L in the lowest quintile and 85 nmol/L in the highest.
A multivariate analysis of women of all ages revealed no significant relationship between early AMD and vitamin D intake (OR for the highest versus the lowest quintile 0.79, 95% CI 0.50 to 1.24). But there was a significant interaction with age (P=0.002). High vitamin D blood levels were associated with a decreased risk for development of early AMD among women younger than age 75 and an increased risk in women aged 75 years or older. Further adjustment for body mass index and recreational physical activity weakened this association in women younger than 75.
Also in women younger than 75, increased intake of vitamin D from foods and supplements combined was associated with lower odds of early AMD -- consuming at least 18µg/day was associated with 59 percent lower odds of developing the condition (OR 0.41, 95% CI 0.20 to 0.78). The authors noted that that level of intake equals 720 IU/day, which exceeds to Institute of Medicine's recommendation for 600 IU/day.
There was no association between time spent in direct sunlight and the likelihood of developing macular degeneration.
The authors write that more studies are needed to verify this association prospectively as well as to better understand the potential interaction between vitamin D status and genetic and lifestyle factors with respect to risk of early AMD.