The elderly with minimal sunshine exposure, some ethnic groups, such as minorities with darker skin, and those who habitually wear clothing that covers most of the skin while outdoors, are particularly vulnerable, said the Scientific Advisory Committee on Nutrition (SACN), which produced the report published today (July 22)
It had been assumed that, for most people, the amount of vitamin D produced by exposure to sunlight containing ultraviolet (UV) B radiation (the main source of vitamin D in the body through skin synthesis) would be sufficient to achieve concentrations of an essential pre-hormone in the body called serum 25(OH)D at or above 25nmol/litre during winter. According to the SACN report, this is now known not to be the case.
SACN also found that musculoskeletal health (based on rickets, osteomalacia – soft bones due to vitamin D insufficiency – falls and muscle strength) was the health outcome identified as the basis for setting dietary reference values (DRVs) for vitamin D.
The evidence overall suggests that the risk of poor musculoskeletal health is increased at serum 25(OH)D concentrations below 25nmol/litre. To protect musculoskeletal health, it is recommended that the serum 25(OH)D concentration of people should not fall below 25nmol/litre at any time of the year.
SACN proposed that a Reference Nutrient Intake (RNI) for vitamin D of 10μg/day for those in the UK population aged four years and over. This is the amount needed for 97.5% of the population to maintain a serum 25(OH)D concentration of 25nmol/litre or above when UVB sunshine exposure is minimal. SACN added that data was insufficient to set RNIs for infants and children aged 0–3 years. As a precaution, a ’Safe Intake’ of vitamin D was proposed for these ages: in the range 8.5–10μg/day for ages 0 to < 1 year (including exclusively breast-fed infants); and 10μg/day for ages 1 to < 4 years.
Since it is difficult to achieve the RNI/Safe Intake from natural food sources alone, it is recommended that consideration is given to strategies for the UK population to achieve the RNI of 10μg/day for those aged four years and older and for younger children to achieve a Safe Intake in the range 8.5–10μg/day at ages 0 to < 1 year and 10μg/day at ages 1 to < 4 years.
Dietary sources of vitamin D in the UK are natural food sources, fortified foods and supplements. There are few naturally rich food sources of vitamin D.
Meat and meat products
According to the National Diet and Nutrition Survey, meat and meat products are the main contributor to vitamin D in all age group except children under three years, providing 23–35% of intake. Across all age groups, ‘fat spreads’, most of which are fortified with vitamin D, contribute 19–21% and cereals/cereal products 13–20% (some breakfast cereals are fortified and fats and eggs used as ingredients contribute to other foods in this group).
Fish and fish dishes made a greater contribution to vitamin D intakes in adults (17–23%) than children (8–9%). Milk and milk products are the major source in children aged 1.5–3 years (24% of intake) and infant formula in non-breast fed infants aged 4–18 months.
The highest average intakes are in bottle-fed infants under one year of age (typically 7.5–9.8μg/day), as formula milks are fortified with vitamin D. In other children and adults, average daily intakes are much lower at around 2μg/day in younger children, around 2–2.5μg/day in older children and 3–5μg/day in adults, the highest average intakes being in adults over 65 years who took supplements of vitamin D (at just over 5μg/day).
“We welcome SACN’s thorough review of the evidence base in its draft report,” said Sara Stanner, science director at the British Nutrition Foundation. “There are few natural food sources of vitamin D (meat, eggs, oily fish). Given current intake levels of vitamin D from foods, at less than 5μg/day, the draft recommendation of 10μg is unlikely to be achievable from these foods alone, particularly for groups where there is advice to limit oily fish consumption to two servings a week (eg girls and pregnant women).”