Vitamin D

Vitamin D is the vitamin that we get from the sun. It is actually not considered a true vitamin but a pro-hormone created by the action of sunlight on the skin and then activated by the liver and kidneys. The activated form of vitamin D has a number of functions within the body, one of the most important being the regulation of the body’s calcium levels. Vitamin D enhances calcium absorption and ensures the development and growth of strong bones and teeth.

Vitamin D deficiency is actually more common than people realise and is starting to become an Australian public health issue as sun safe, anti-cancer messages, decreases our populations sun exposure. Other factors such as spending most of the time indoors, total body covering for cultural or religious reasons,  or living at latitudes far from the equator can also reduce sunlight exposure and subsequent vitamin D production. People with dark skin have reduced vitamin D production compared to fairer skinned people and older people are also at risk of vitamin D deficiency as the ability for vitamin D production by the skin reduces with age.

In children, vitamin D deficiency results in the disease rickets. This is where the child’s bones weaken and bow due to failure of the skeleton to properly mineralise with calcium. In adults, the lack of calcium due to vitamin D deficiency leads to a disease caused osteomalacia, which means ‘soft bones’. This makes them more prone to fracture, especially in the hip and spine.

Food Sources of Vitamin D

About 80-100% of a person’s vitamin D requirements are met by the action of sunlight on the skin and if sunlight exposure is adequate then vitamin D intake through food may be considered unnecessary.

Food sources of vitamin D include fatty fish (sardines, tuna, salmon and mackerel), cod liver oil, eggs, fortified milk, margarine and breakfast cereal. Most of these foods only contain a small amount of vitamin D and it is almost impossible to receive all of a person’s daily requirements from food alone. It may be necessary to take a supplement if sun exposure is limited.

How Much Vitamin D Do We Need?

The Adequate Intake (AI) level for Vitamin D is 5ug/day for people aged 19-50 years, 10ug/day for people aged 51-70 years and 15ug/day for those aged 71 and above (NHMRC).

Vitamin D is a fat soluble vitamin and thus it can be stored by the body for later use when skin production may be low. For example, adequate sun exposure during summer time can store enough vitamin D to last through a winter with little or no sun exposure. Research estimates that for an older woman with fair skin exposure of 6% of the body surface (face, forearm and hands) to 15-30 minutes of sunlight, 2-3 times er week would provide the equivalent of 15ug/day of vitamin D. More or less sun exposure would be required depending on the colour of your skin, age and the latitude of where you live.

Meal and Snack Ideas

  • Have 1-2 serves of fatty fish (tuna, salmon, sardines etc) a week
  • Buy fortified milks and breakfast cereals
  • cod liver oil
  • see an Accredited Practicing Dietitian to see if a supplement is right for you.

Too Much of a Good Thing?

Vitamin D toxicity can occur from excessive intake from supplements. It cannot occur through excess sun exposure or from natural dietary sources. An Upper Limit (UL) of 50ug/day has been set.

References:
  • Nutrient Reference Values for Australia and New Zealand, National Health and Medical Research Council
  • Wardlaw’s Perspectives in Nutrition 8th Edition, Byrd-Bredbenner, 2009.
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About Kate Freeman
Kate Freeman is a Registered Nutritionist who is passionate about providing honest, simple nutrition advice and doing it in such a way that inspires and motivates you to make positive lifestyle changes to achieve your health and nutritional goals. She's married with 2 children and live in New South Wales, Australia.

2 Responses to Vitamin D

  1. Pingback: Vitamin K « Kate Freeman Nutrition

  2. Pingback: Folate « Kate Freeman Nutrition

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