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Mean responses of serum 25OHD level to total vitamin D intake in the winter seasons at latitudes 49.5°N (Europe) and 78°S (Antarctica) for ages 6 to > 60 years (Ala-Houhala et al., 1988; Van Der Klis et al., 1996; Schou et al., 2003; Larsen et al., 2004; Viljakainen et al., 2006, 2009; Cashman et al., 2008, 2009; Smith et al., 2009; see Table 5-4 for summary of studies) were analyzed by regression using mixed effect model following log transformation controlling for study effect by a random effects model because there was no effect of age on the response of serum 25OHD level to total intake of vitamin D. The relationship for achieved vitamin D is y achieved 25OHD in nmol/L = 9.9 ln (total vitamin D intake) (shown as solid line) with predicted CIs (shown as two dashed lines) for lower interval of y = 8.7 ln (total vitamin D intake) and upper interval of y = 11.2 ln (total vitamin D intake). This regression explains 72 percent of the within-study variability and 96.4 percent of the between-subject variability.

NOTE: Log (total vitamin D intake) was back-transformed to total vitamin D intake for presentation in this figure.