Vitamin D and Health

9.36 Data from two of these RCTs 95 (Cashman et al., 2008; Cashman et al., 2009) were from adults in the
South of the Republic of Ireland (latitude 51 o N) and Northern Ireland (latitude 55 o N) (NDNS shows that
mean serum 25(OH)D concentrations in older adults were ~10 nmol/L lower in the Northern region of
UK [55-57ºN] than in London and the South East [51ºN]). The RCT in adolescent girls (Cashman et al.,
2011b) was conducted at 55 o N and 60 o N (Copenhagen, Denmark, and Helsinki, Finland, respectively)
representing latitudes in the UK from Edinburgh to the Shetlands. The total vitamin D intake range in
the RCTs was specifically selected to provide a range within the current 2.5 th and 97.5 th percentiles of
intakes for UK adults/older adults (NDNS). The vitamin D intakes of the girls are comparable to those
for girls in the UK. The same RCT data were used by the German Nutrition Society in setting the
DACH 96 country recommendations for vitamin D but using 50 nmol/L as their basis (German Nutrition
Society, 2012).
Further considerations in setting DRVs for vitamin D using the RCTs data
9.37 The RNI is notionally an intake of a nutrient that is two SDs above the EAR and is therefore derived
from a known EAR and the variance around the distribution. In relation to vitamin D, especially the
vitamin D intake-serum 25(OH)D concentration relationship, there are sufficient data to estimate
directly the vitamin D intake required to maintain serum 25(OH)D concentration above a selected
concentration (i.e., 25 nmol/L), over winter, in 97.5% of the population (i.e., the RNI). This direct
estimation avoids the requirement to add two SDs to the EAR, which is an approximation 97 .
9.38 Full details of the regression and mathematical modelling used to derive these intake estimates are
provided in the three publications (Cashman et al., 2008; Cashman et al., 2009; Cashman et al., 2011b)
but, in brief, the aim of the modelling was to describe the conditional distribution of serum 25(OH)D
concentrations at specific values of vitamin D intake in each of the three population subgroups
separately. A regression model was used to estimate the variation in serum 25(OH)D concentrations
about the mean and Q-Q plots 98 were used to examine the assumption that variation about the
predicted value was normally distributed. The distribution for serum 25(OH)D concentration as a
function of total vitamin D intake was obtained for each of the three population subgroups separately
(see Figure 8 below, as an example). Finally, the dietary requirements for vitamin D to maintain
selected percentages of the population above specific serum 25(OH)D concentrations were estimated.
In all three age-groups, results were verified using robust regression models that minimised the effect
of outliers and heteroscedasticity 99 .
95 These RCTs were specifically commissioned and funded by the Food Standards Agency to inform considerations on whether the DRVs for vitamin D
(DH, 1991) required re-evaluation.
96 [D-A-CH arises from initial letters of the common country identification for the countries Germany (D), Austria (A) and Switzerland (CH)].
97 While the EAR is a constituent value within the DRV, the EAR does not exist at the threshold serum 25(OH)D concentration of 25 nmol/L for adults
20-40 y and adults 64+ y.
98 Quantile-Quantile plot is a graphical method for comparing two probability distributions.
99 Occurs when variance around the regression line is unequal across the range of values of the predictor variable.
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