Commonly recommended daily intake of vitamin D is not sufficient if sunlight exposure is limited

J Intern Med. 2000 Feb;247(2):260-8. doi: 10.1046/j.1365-2796.2000.00595.x.


Objectives: Sunlight exposure of the skin is known to be the most important source of vitamin D. The aims of this study were: (i) to estimate vitamin D status amongst sunlight-deprived individuals (veiled Arab women, veiled ethnic Danish Moslem women and Danish controls); and (ii) through food intake analysis to estimate the oral intake of vitamin D necessary to keep a normal vitamin D status in sunlight-deprived individuals.

Design: Cross-sectional study amongst randomly selected Moslem women of Arab origin living in Denmark. Age-matched Danish women were included as controls. To control for racial differences, a group of veiled ethnic Danish Moslem women (all Caucasians) was included.

Setting: Primary Health Care Centre, City Vest and Department of Endocrinology and Metabolism C, University Hospital of Aarhus, Aarhus Amtssygehus, Aarhus, Denmark.

Subjects: Sixty-nine Arab women (60 veiled, nine non-veiled) and 44 age-matched Danish controls were randomly selected amongst patients contacting the primary health care centre for reasons other than vitamin D deficiency. Ten ethnic Danish Moslem women were included through a direct contact with their community.

Main outcome measures: Serum levels of 25-hydroxyvitamin D were used as estimates of vitamin D status. Intact parathyroid hormone (PTH) was used to control for secondary hyperparathyroidism. Alkaline phosphatase and bone-specific alkaline phosphatase were used as markers for osteomalacic bone involvement. Oral intake of vitamin D and calcium were estimated through a historical food intake interview performed by a trained clinical dietician.

Results: Veiled Arab women displayed extremely low values of 25-hydroxyvitamin D: 7.1 +/- 1.1 nmol L-1, compared with 17.5 +/- 2. 3 (P < 0.002) in ethnic Danish Moslems and 47.1 +/- 4.6 (P < 10-17) in Danish controls. PTH was increased amongst veiled Arab women: 15. 6 +/- 1.8 pmol L-1, compared with 5.7 +/- 1.4 in ethnic Danish Moslems and 2.7 +/- 0.3 (P < 10-6) in Danish controls. The vitamin D intake (including food supplementation) was very low amongst Arab women: 1.04 microg day-1, compared with 13.53 amongst ethnic Danish Moslems and 7.49 amongst Danish controls (P < 0.0005).

Conclusions: Severe vitamin D deficiency is prevalent amongst sunlight-deprived individuals living in Denmark. In veiled Arab women, vitamin D deficiency is the result of a combination of limitations in sunlight exposure and a low oral intake of vitamin D. The oral intake of vitamin D amongst veiled ethnic Danish Moslems was, however, very high, at 13.53 microgram (approximately 600 IU), but they were still vitamin D-deficient. Our results suggest that the daily oral intake of vitamin D in sunlight-deprived individuals should exceed 600 IU; most probably it should be 1000 IU day-1 to secure a normal level of 25-hydroxyvitamin D. This finding is in contrast with the commonly used RDA (recommended daily allowance) for adults in Europe: 200 IU day-1.

MeSH terms

  • Adult
  • Alkaline Phosphatase / blood
  • Arabs*
  • Calcium / blood
  • Calcium / urine
  • Case-Control Studies
  • Clothing / adverse effects*
  • Creatinine / blood
  • Cross-Sectional Studies
  • Denmark / ethnology
  • Feeding Behavior
  • Female
  • Humans
  • Hydroxyproline / urine
  • Hyperparathyroidism, Secondary / blood
  • Hyperparathyroidism, Secondary / diagnosis
  • Magnesium / blood
  • Nutrition Policy
  • Parathyroid Hormone / blood
  • Phosphates / blood
  • Sunlight*
  • Ultraviolet Rays
  • Vitamin D / administration & dosage*
  • Vitamin D / analogs & derivatives*
  • Vitamin D / blood
  • Vitamin D Deficiency / blood
  • Vitamin D Deficiency / etiology*


  • Parathyroid Hormone
  • Phosphates
  • Vitamin D
  • 25-hydroxyvitamin D
  • Creatinine
  • Alkaline Phosphatase
  • Magnesium
  • Hydroxyproline
  • Calcium