*3.4. Predictors of D3 Production*

Using the best subsets method with the log of D3 production (change from baseline to peak) as the dependent variable and age, baseline serum D3 concentration, fat mass, lean mass, reported vitamin D intake and reported sun exposure history entered as independent variables, the single best predictor of D3 production was age (*r2* = 0.238). The best pairs of predictors were age and lean body mass (*r2* = 0.30) and age and baseline serum D3 concentration (*r2* = 0.298). Age, baseline serum D3 concentration and lean body mass were the best triplet of predictors (*r<sup>2</sup>* = 0.352). Fat mass, reported time spent outside and vitamin D intake were not selected as predictors until four, five or six predictors were entered, and contributed little to the model.
