Vitamin D is a bit of an interesting vitamin as it acts as more like a hormone within the body.
There are two main forms of vitamin D:
- D2 (ergocalciferol)
This is the form of vitamin D found in some supplements.
- D3 (cholecalciferol)
This is the form of vitamin D created by the action of sunlight reacting with a cholesterol molecule in our skin. It is also found in a limited number of foods such as oily fish, egg yolks, butter and fortified foods as well as some supplements.
Vitamin D is responsible for:
- Maintaining strong bones and teeth (by tightly controlling calcium and phosphorus levels within the body)
- Promoting normal cell division during growth and development
- Potential role in the prevention of certain cancers as well as promoting a healthy immune system
- Rickets in children
- Osteoporosis and increased risk of fractures in adults
We are constantly learning more about the role of vitamin D in the body, with recent studies indicating a potential link between vitamin D deficiency and increased risk of:
- diabetes (Hypponen et al 2001)
- heart disease (Hashemi et al 2015)
- autoimmune conditions (e.g. MS) (Eskandari et al 2015)
- depression (Mizoue et al 2015 and Polak et al 2014) and other mental health conditions
- some cancers (especially colon cancer) (Garland et al 2009).
How much vitamin D/sunshine do I need?
Australian guidelines recommend the following amounts of vitamin D (NHMRC 2006):
Adults under 50 years of age: 5µg/d (200IU/d)
Adults over 50 years of age: 10µg/d (400IU/d)
Adults over 70 years of age: 15µg/d (600IU/d)
As you can see, it is very difficult to consistently achieve an adequate intake of vitamin D every single day through diet alone:
100g salmon (canned or fresh) 13µg vitamin D
a small can of tuna 4µg vitamin D
1 egg yolk 1µg vitamin D
250ml fortified dairy/soy milk 5µg vitamin D
The best source of vitamin D is therefore sunshine!
Although increased sun exposure is believed to place you at greater risk of skin cancer, SunSmart Australia recommends the following level of sun exposure to achieve and maintain adequate vitamin D levels:
It should also be noted that there are a number of variables impacting upon your body’s ability to ‘absorb’ the necessary vitamin D from sunshine.
Firstly, different geographical locations, level of cloud cover and seasonal changes impact upon how much sun exposure you will need.
Secondly, the following people are especially prone to vitamin D deficiency:
- Those with darker skin
- Those wearing full covered clothing (e.g. for religious reasons) or sunscreen every day
- Patients in long-stay hospital care
- Elderly in aged care facilities
- Office workers
- Those suffering from certain medical conditions (e.g. chronic kidney or liver diseases)
Christakos et al (2010), ‘Vitamin D: Metabolism’, Endocrinology and Metabolism Clinics of North America, 39(2): 243-253.
Eskandari et al (2015), ‘Comparisons of serum vitamin D level in multiple sclerosis patients, their siblings, and healthy controls’, Iranian Journal of Neurology, 14(2): 81-85.
Garland et al (2009), ‘Vitamin D for cancer prevention: global perspective’, Annals of Epidemiology, 19(7): 468-483.
Hashemi et al (2015), ‘Effect of vitamin D therapy on endothelial function in ischemic heart disease female patients with vitamin D deficiency or insufficiency: A primary report’, ARYA Atherosclerosis, 11(1): 54-59.
Hypponen et al (2001), ‘Intake of vitamin D and risk of type 1 diabetes: a birth-cohort study’, Lancet, 358(9292): 1500-1503.
Mizoue et al (2015), ‘Low serum 25-hydroxyvitamin D concentrations are associated with increased likelihood of having depressive symptoms among Japanese workers’, Journal of Nutrition, 145(3): 541-546.
NHMRC (2006), Vitamin D, available from: https://www.nrv.gov.au/nutrients/vitamin-d.
Polak et al (2014), ‘Serum 25-hyrdroxyvitamin D concentrations and depressive symptoms among young adult men and women’, Nutrients, 6(11), 4720-4730.
SunSmart, How much sun is enough?, available from: http://www.sunsmart.com.au/vitamin-d/how-much-sun-is-enough.