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Vitamin D has many important roles in the body including helping with calcium absorption, cell growth and maintaining a healthy immune system to fight disease and illness.

Find out about these important roles as well as vitamin D deficiency, how to test for vitamin D deficiency and where to get vitamin D.

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The importance of vitamin D

Vitamin D is essential for bone health. It helps increase the absorption of calcium from the stomach, regulates the amount of calcium in the blood and strengthens the skeleton.

The main source of vitamin D is production in the skin after exposure to sunlight. Small amounts of vitamin D are available in some foods. For vitamin D to work effectively it needs to be activated by the liver and kidney, which then turns it into a hormone.

Vitamin D has many roles within the body. The most understood role is its ability to help the body absorb calcium and phosphorus and vitamin D also assists with:

  • bone development and strength
  • cell growth
  • maintaining a healthy immune system
  • hormone function
  • nervous system regulation

Apart from its important role in maintaining bone health, vitamin D may also have an important role in other diseases such as diabetes, cancer and infection. These are currently areas of intense research.

Vitamin D deficiency

Vitamin D deficiency is a common condition in Australia, affecting a large number of women.

The body's main source of vitamin D comes from the skin being exposed to UV radiation in sunlight. When sunlight hits the skin, it reacts with a cholesterol-like substance and produces vitamin D. The amount of sun exposure needed depends on your skin colour, where you live and the time of year.

Even though Australia has one of the highest UV radiation levels in the world and is well known for its abundance of sunshine, research has found many people are deficient in vitamin D because of the amount of time they spend indoors.

Those at most risk of having a vitamin D deficiency include:

  • older people and people living in care (such as hospitals or rehabilitation) – particularly those who stay indoors or cannot walk and have limited exposure to the sunlight
  • people with gastrointestinal disease
  • people taking certain medications (e.g. anti-epileptics)
  • people who cover or veil their skin for religious or cultural reasons
  • dark-skinned people
  • pregnant women
  • postmenopausal women

Vitamin D levels are seasonal and fall in the winter and early spring when people are less likely to be outdoors.

How do you know what your vitamin D level is?

Vitamin D levels can be measured through a simple blood test.

Vitamin D levels are classified into ranges. The Australian and New Zealand Bone and Mineral Society, the Endocrine Society of Australia and Osteoporosis Australia (2005) state that adult serum 25-OHD levels show:

Level of vitamin D deficiency Range (in nmol/L - a measure of the molecular chemistry)
Mild

25-50

Moderate

12.5-25

Severe

Less than 12.5

Where to get vitamin D

Sunlight

What you need:

Usually 10-15 min exposure to outdoor sun per day is necessary for the production of adequate vitamin D.
As a general guide expose face, arms, hands or legs for:

  • 10 minutes in summer
  • 5-20 minutes in spring and autumn
  • 30 minutes in winter

Check the map of Australia for guidelines on the recommended amount of sun exposure based on your location, the season and your skin pigmentation.

You can get daily updates on the UV index at: sunsmart.com.au

What to be careful of:

  • Avoid excessive exposure to sunlight, particularly in summer because of the risk of skin damage and skin cancers
  • Don't use solariums as a substitute for sunlight because the UV radiation in solariums:
    • doesn't help to produce vitamin D
    • will not help with vitamin D deficiency
    • increases your risk of skin cancer

Diet

What you need:

Dietary sources of vitamin D are limited and can come from:

  • plants (vitamin D2) such as mushrooms – shitake and button mushrooms are good options
  • animal sources (vitamin D3) such as liver, fish (tuna, salmon, sardines, herring and mackerel) and egg yolk – one egg can supply 10% of your daily intake
  • fortified foods (boosted) with vitamin D such as milk, soy drinks, margarine, breads and cereals

What to be careful of:

It is very hard to get adequate amounts of vitamin D from these sources alone.

Supplements

What you need:

For the elderly who are in care, taking additional vitamin D supplements and calcium supplements may reduce the incidence of fracture[1].

What to be careful of:

Get your doctor's advice about whether to take a vitamin D supplement after you have been tested.

What you need to know

  • Vitamin D helps with bone health
  • Exposure to sunlight each day is important to maintain vitamin D levels
  • See your doctor to have a blood test to determine your level of vitamin D
  • If you are vitamin D deficient, it may be necessary to take a vitamin D supplement
  • Your treating doctor can recommend whether you need to take a vitamin D supplement

References

  • 1
    Papadimitropoulos E, Wells G, Shea B, Gillespie W, Weaver B, Zytaruk N et al. Meta-analyses of therapies for postmenopausal osteoporosis. VIII: Meta-analysis of the efficacy of vitamin D treatment in preventing osteoporosis in postmenopausal women. Endocr.Rev. 2002;23(4):560-9.
Last updated: 16 January 2020 | Last reviewed: 01 December 2013

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