 Moderating effect of sex and age groups was tested by adding interaction terms to separate multivariable mixed-effects regressions 3-way and 4-way interaction terms between Time, exposure, Age group and sex and stratifying by sex and age group to examine relationships among the following groups: 1 Younger men, 2 Older men, 3 Younger women, 4 Older women, whenever at least one 4-way interaction was deemed statistically significant. Further, moderating effects by race were also examined using a similar approach 1 Whites, 2 African-Americans Supplemental method 2, given the well-known higher prevalence of vitamin D deficiency among African-Americans compared with Whites and the differential rates of increases in vitamin D status recently shown by age, sex and race groups.43 Variable time of follow-up is accounted for in the mixed-effects regression model as annual rate of change in the outcome was of primary interest. 