Vitamin D and Health

Review of DRVs
10.47 The DRVs describe the distribution of requirements in a population and comprise 3 estimates: the
Estimated Average Requirement (EAR), half of a group in a population will need more than this
amount and half will need less; the Reference Nutrient Intake (RNI), the amount that will meet the
needs of 97.5% of the population; and the Lower Reference Nutrient Intake (LRNI), the intakes which
will meet the needs of only 2.5% of the population.
10.48 Previously in the UK, an RNI (but not an EAR or LRNI) for vitamin D was set only for population groups
at high risk of deficiency (DH, 1991). It was assumed that, for most people, the amount of vitamin D
produced by exposure to sunlight containing UVB in the summer months would be adequate for
achieving serum 25(OH)D concentrations ≥ 25 nmol/L during winter. It is now known that this is not
the case.
10.49 In the current review, musculoskeletal health was used as the basis for setting DRVs for vitamin D.
The available data were not sufficient to establish a distribution of serum 25(OH)D concentrations that
would be required to set the 3 DRV estimates for vitamin D intake (i.e., LRNI, EAR, RNI) or to identify a
clear threshold serum 25(OH)D concentration to support musculoskeletal health outcomes. However,
the evidence overall suggests that risk of poor musculoskeletal health increases at serum 25(OH)D
concentrations below 25 nmol/L. A serum 25(OH)D concentration ≥ 25 nmol/L was therefore
considered to be a ‘population protective level’; i.e., the concentration that 97.5% of individuals in the
UK should achieve, or be above, in terms of protecting musculoskeletal health.
10.50 A serum 25(OH)D concentration of ≥ 25 nmol/L was selected as the basis for deriving the RNI for
vitamin D; i.e., the mean vitamin D intake required to achieve a serum 25(OH)D concentration
≥ 25 nmol/L by 97.5% of the population. The next step was to estimate the average dietary intake
value that would achieve a serum 25(OH)D concentration ≥ 25 nmol/L in 97.5% of the population in
the UK and thereby define the RNI for vitamin D. Only an RNI was established because this
precautionary protective approach prohibited establishment of an EAR or LRNI. The average vitamin
D intake refers to the mean or average intake over a period of time (e.g., 1 week) and takes account of
day to day variations in vitamin D intake.
10.51 Sun exposure is the major source of vitamin D during the summer months for the majority of people in
the UK and most achieve a serum 25(OH)D concentration > 25 nmol/L in summer. A modelling
exercise was carried out to estimate the summer sunshine exposure required to maintain serum
25(OH)D concentrations ≥ 25 nmol/L during winter. However, it was not possible to quantify the
sunlight exposure required in the summer months to maintain a winter serum 25(OH)D concentration
of ≥ 25 nmol/L because of the number of factors that affect endogenous vitamin D synthesis, storage
and utilisation. It was, therefore, not possible to take account of sunlight exposure in setting the RNI.
10.52 The RNI for vitamin D was estimated by modelling data from individual vitamin D RCTs in adults (men
& women, 20-40 y and ≥ 64y) and adolescent girls (11 y). The RCTs were conducted in winter so that
skin production of vitamin D was minimal. The modelling exercise indicated that the estimated
average daily vitamin D intake required to maintain serum 25(OH)D concentration ≥ 25 nmol/L in
winter by 97.5% of the population is 12 µg (480 IU) based on serum 25(OH)D analysis by LC-tandem
MS or 9 µg (360 IU) based on analysis of the same sera by immunoassay. Since the target threshold
serum 25(OH)D concentration of 25 nmol/L was based on studies which had used a range of different
assays to measure serum 25(OH)D concentration the RNI was set between these 2 estimates, at
10 µg/d (400 IU).
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