What Causes Vitamin D Insufficiency

Vitamin D insufficiency is more common than once thought and is becoming a real concern. Unlike many other vitamins, Vitamin D is not only taken in through the diet but is also produced and stored in the body. The action of the sun on the skin is required for the body to synthesise Vitamin D and adequate exposure to sunlight is required to do so. As such, the body’s own production of Vitamin D relies on receiving enough exposure to sunlight.1 However, it is believed that even in summer, when there is higher UV exposure, 1 in 3 Australians may have low Vitamin D levels.

Dietary intake of Vitamin D is also estimated to be well below the recommended adequate intake level for most Australians. Vitamin D is available through a relatively small number of foods and dietary sources alone rarely provide enough Vitamin D. The best food sources of Vitamin D are fatty fish and fortified milks and cereals.

The combination of low dietary intake and inadequate sun exposure are major factors contributing to widespread Vitamin D insufficiency, but what are some other risk factors for Vitamin D insufficiency?

  • Age – in older people the ability of the skin to synthesise Vitamin D is significantly less than in younger people. A person 70 years of age exposed to the same amount of sunlight as a 20 year old person makes approximately 25% of the Vitamin D3 that the 20 year old person is able to make.2
  • Working indoors or covering up excessively when outside – these people have low exposure to natural sunlight and may require additional dietary Vitamin D.
  • Sunscreen use – sunscreen almost completely reduces the skin’s ability to synthesise Vitamin D. However, for fair skinned people sensible sun protection behaviour should not put them at risk of Vitamin D insufficiency.
  • Season – less exposure to sunlight in winter means less opportunity for the body to produce Vitamin D. In winter and spring 40.5% of women under 60 years in south-east Queensland showed insufficient levels of Vitamin D.
  • Darker skin pigmentation – Adults and children with darker pigmentation in their skin may have a reduced synthesis of Vitamin D.
  • Pregnancy and lactation – The requirement for Vitamin D increases in pregnant women due to calcium requirements and bone mineralisation in the developing baby. Even low risk women are commonly Vitamin D insufficient when pregnant.
  • Infants – infants who are breastfed and dark skinned may require Vitamin D supplementation to maintain adequate Vitamin D nutrition. Unfortunately breast milk is a poor source of Vitamin D. The most important factor for the development of Vitamin D insufficiency in infants is the status of the mothers Vitamin D.
  • Children – Vitamin D is needed for optimal bone mineralisation in children especially during times of rapid growth or when sunlight exposure is limited.1 This may include during the winter months and where there is excessive use of sunscreen or coverings when outside.
  • Reduced absorption of nutrients in the gut – some people may have an inability to absorb some nutrients and fat soluble vitamins such as Vitamin D.
  1. Braun L., Cohen M; Herbs & Natural Supplements: An evidence based guide, 3rd Edition; Elsevier; Australia; 2010
  2. Holick, M. F. “Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and for cardiovascular disease”. American Journal of Clinical Nutrition. Vol. 80, No. 6 Suppl. (Dec 2004), pp. 1678S-88S.