Vitamin D and Health

dietary vitamin D requirements.
5.15 Most observational studies which have examined serum 25(OH)D concentration of breast fed infants
are not relevant to the UK. However, a cross-sectional study in New Zealand (Wall et al., 2013) found
significant seasonal variations in serum 25(OH)D concentration of healthy term exclusively breast fed
infants (n=94; mean age, 10 weeks). Median serum 25(OH)D concentration was significantly lower
(p=0.0001) in infants enrolled in winter (21 nmol/L; IQR 37 , 14-31 nmol/L) compared to those enrolled
in summer (75 nmol/L; IQR, 55-100 nmol/L), autumn (49 nmol/L; IQR, 30-64 nmol/L) or spring
(60 nmol/L; IQR, 40-79 nmol/L). Overall, 60% of infants whose serum 25(OH)D concentration was
measured in winter had a concentration < 25 nmol/L compared with 4% in summer. However, serum
25(OH)D concentrations were higher in spring than in autumn, which was unusual. Since the study
was cross-sectional, the effects over time of exclusive breast feeding on infant serum 25(OH)D
concentration could not be assessed. Information was not available on sun exposure of the infant and
maternal serum 25(OH)D concentration during the last trimester of pregnancy was not measured.
Relationship between vitamin D intake and serum 25(OH)D concentration by ethnicity
5.16 Data on dose-response effects of vitamin D intake on serum 25(OH)D concentration of individuals
from ethnic groups in the UK are lacking.
5.17 Findings from RCTs in the USA, which have examined the effect of vitamin D supplementation on
African Americans are conflicting (Gallagher et al., 2013; Gallagher et al., 2014; Ng et al., 2014). Based
on their findings from a 4-arm RCT (placebo, 25 µg/1000 IU, 50 µg/2000 IU, or 100 µg/4000 IU vitamin
D 3 daily for 3 months), Ng et al. (2014) estimated that 41 µg/d (1640 IU/d) of vitamin D was required to
maintain winter plasma 25(OH)D concentrations > 50 nmol/L in 97.5% of African American men and
women (n=292; age, 30-80y). This is almost twice the amount established by the IOM (15-20 µg/600-
800 IU per day) based on data from RCTs with white people. However, since the study did not include
a group with white skin, it is not certain that there are differences in requirements by skin type.
5.18 In contrast, Gallagher et al. (2013) reported that the increase in serum 25(OH)D concentration after
daily vitamin D 3 supplementation (placebo, 10 µg/400 IU, 20 µg/800 IU, 40 µg/1600 IU, 60 µg/2400 IU,
80 µg/3200 IU, 100 µg/4000 IU, or 120 µg/4800 IU for 12 months) in older African American women
(n=110; mean age, 67y) was similar to that observed in white women (n=163; mean age, 67y) in a
similarly designed RCT (Gallagher et al., 2012) and that 20 µg (800 IU) per day of vitamin D was
required to maintain 25(OH)D concentration > 50 nmol/L in 97.5% of African American and white
women.
5.19 Another RCT by the same group (Gallagher et al., 2014), which was conducted in younger white and
African American women with serum 25(OH)D concentration ≤ 50 nmol/L (n=198; mean age 36.7y)
and who were assigned to receive placebo or vitamin D 3 (10 µg/400 IU, 20 µg/800 IU, 40 µg/1600 IU
or 60 µg/2400 IU) daily for 12 months, reported that mean baseline serum 25(OH)D concentration was
lower in African American women (29 nmol/L) than the white women (36.4 nmol/L). However, as the
absolute increase in serum 25(OH)D concentration after vitamin D supplementation was greater in
African American women than in white women, the mean serum 25(OH)D concentration after 12
months was similar in both races at higher doses. It was estimated using mathematical modelling that
10 µg/d (400 IU/d) of vitamin D was required to increase 25(OH)D concentrations > 50 nmol/L in 97.5
% of the white women and between 20 and 40 µg/d (800 and 1600 IU/d) of vitamin D was required to
37 Inter-quartile range.
37