Position statement by the Scientific Advisory Committee on Nutrition 2007
from SACN website at www.sacn.gov.uk
Summary from PDF
1. The main source of vitamin D in man is usually considered to be skin photosynthesis following irradiation with short wavelength ultra violet light (290-310 nm). Vitamin D is also found in a few foods, such as oily fish, fortified margarines and some breakfast cereals and there are smaller amounts in red meat and egg yolk.
2. 25-hydroxyvitamin D (25(OH)D) is the major circulating metabolite of vitamin D and plasma levels of this metabolite serve as an indicator of vitamin D status. Traditionally a plasma 25(OH)D concentration less than 25nmol/l (10ng/ml) has been regarded an index of suboptimal vitamin D status. Recently higher thresholds have been proposed though the functional outcomes associated with them are currently unclear. Moreover, laboratory methodology for plasma 25(OH)D measurement is not well standardized.
3. Several factors potentially affect vitamin D status. These include genetic factors, adiposity and factors affecting the cutaneous synthesis of vitamin D such as skin pigmentation, age, season, latitude, melanin concentration, clothing and use of sunscreens. Seasonal variations in vitamin D status are observed in the UK where the 2000 National Diet and Nutrition Survey (NDNS) reported average plasma 25(OH)D concentrations to be highest in July- September and lowest in January-March. During winter, the UK population relies on body stores and dietary vitamin D to maintain vitamin D status. Solar UV radiation varies with latitude, and in winter months at latitudes of about 52o and above, there is no ultraviolet light of the appropriate wavelength for the cutaneous synthesis of vitamin D. For the remaining months, more than half the effective UV radiation occurs between certain times (1100 and 1500 hours) and is lower in the north than the south. Skin exposure to UV irradiation of the appropriate wavelength is essential for maintaining adequate vitamin D status and a clear recommendation on length and intensity of exposure is required.
4. The NDNS provides evidence of low vitamin D status, as defined by a plasma 25(OH)D concentration less than 25nmol/l, in most age groups in the UK population, especially older children and young adults, and in older people living in institutions. Young women of childbearing age also have low vitamin D status and are likely to begin their pregnancies with low stores. Other evidence highlights a greater risk of vitamin D deficiency in population subgroups, particularly infants from black and ethnic minority groups. Cases of rickets and hypocalcaemia in UK children, predominantly of Afro- Caribbean or South Asian origin, are widely reported but there are no NDNS data for these population subgroups.
5. The Dietary Reference Values (DRVs) as defined in the 1991 COMA report do not set a Reference Nutrient Intake for vitamin D for adults or children over four years of age who receive adequate sunlight exposure. The current Reference Nutrient Intake (RNI) for
pregnant and breastfeeding women is 10µg (400 IU)3 vitamin D per day.
For children under the age of four years it is 7-8.5µg (280-340 IU) per day and for those in the population aged
over 65 years or confined indoors is 10µg vitamin D per day.
Table 1. Reference Nutrient Intakes (RNI) for vitamin D (µg/d) (Department of Health, 1998)
Age Males Females
0-6 months 8.5 8.5
7 months to 3 years 7 7
4 years to 65 years – –
65+ years 10 10
Pregnancy 10
Lactation, 0-4 months 10
Lactation, 4+ months 10
(recall that 10 ug = 400 IU)
Note: The above RNIs apply to healthy populations. Those at risk of inadequate sunlight exposure may require supplementation.
6. In most instances, these intakes cannot be met from the diet and at the present time can only be guaranteed by supplementation. A recommendation of 10µg (400 IU) a day has been made for pregnant and lactating women and for people over the age of 65 years. Although this has been in place for sometime, there is concern that it is overlooked or not implemented by health professionals and the general public.
7. Deficiency of vitamin D results in rickets and osteomalacia. The incidence of rickets in the UK declined from the 1920s onwards, which can partly be attributed to better living conditions, a reduction in atmospheric pollution, changes in diet, mandatory fortification of margarine with vitamin D and replacement of cow’s milk by infant formula during the first year of life. Rickets and osteomalacia are now reported rarely among the white UK population although there is evidence of significant incidence in UK South Asian and Afro-Caribbean groups. There is also recognition of a high prevalence of low vitamin D status among older people, particularly those living in institutions. However, there are no population-based estimates of incidence and it is likely that many cases do not reach clinical attention. This has implications for long- term health and well-being.
8. A low vitamin D status has been implicated in a range of diseases including osteoporosis, several forms of cancer, cardiovascular disease, tuberculosis, multiple sclerosis and type I diabetes. Osteomalacia and osteoporosis both increase the risk of fracture. Research in these areas is developing, but evidence is inconclusive at present, and further work is needed before any definitive conclusions can be drawn.
At 10 ng/ml the UK is able to reduce incidence of rickets, but not other diseases