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Can a person O.D. on Vitamin D?

 Lately there has been a flurry of reporting about vitamin D deficiency and how this affects health. But as people rush out to stock up on supplements, which type of vitamin D do we need? 

Is there such a thing as having too much?

Julie Godfrey

Julie Godfrey

Vitamin D is needed for the health of bone and teeth, as well as absorption of calcium. It plays a role in immunity, can help reduce inflammation and is being investigated for use in treating cancer. 

Over the years, headlines have linked vitamin D deficiency with chubby children, childhood asthma, auto-immune diseases, type 2 diabetes, cardiovascular disease, slower healing bones and age-related macular degeneration (deterioration of eyesight).

Low levels of vitamin D have also been documented in populations of cancer patients. Groups most vulnerable to deficiency are children under 5 and adults over 65, pregnant and lactating women, dark-skinned individuals and those who do not expose their skin to the sun.  

While only the term vitamin D is generally used, you may have heard D2 and D3 mentioned, so what are these and which version should we take? 

The general consensus is that D3 (cholecalciferol) is the more biologically active form although many supplement companies still churn out D2 (ergocalciferol) in their formulations, and food manufacturers tend to fortify products with it. Still, the addition of vitamin D2 to milk was a key factor in the elimination of childhood rickets in the U.S. Thus, we can conclude that both forms are viable, with D2 perhaps needing a higher dosage. 

Vitamin D can be obtained naturally from oily fish, eggs, dairy products and the sun. Ultraviolet rays act on cholesterol in the skin to form an intermediate product, which is then processed by the liver to produce an active form of the vitamin. Approximately 20 minutes of sun a day can be enough to prevent deficiency. Interestingly, in Costa Rica it used to be customary for people to put their babies out for a half hour in the early morning sun. Grandmother does often know best!

Note that in the same way dark skin blocks a percentage of these rays from filtering through, slapping on the sun block can similarly impair the effectiveness of vitamin D synthesis. Realistically, 20 minutes in the sun is unlikely to be damaging, as long as you avoid the intense 11a.m.-2 p.m. period. 

The amount of vitamin D that we can get from the sun is self-regulated with a built-in system that prevents you from overdosing. Supplementing with tablets or sourcing your vitamin D from fortified foods has no such protection mechanism. Toxicity is important, as a recent report from Copenhagen University linked people with both very low and very high levels of vitamin D in their blood with higher death rates than those with moderate levels.

With the sunny climate of Costa Rica, there should be little need for supplementation. If you do decide to go this route, be aware that D2 is synthesised from plant sources whereas D3 comes from animal sources. As always there is much debate on levels, but children’s daily allowance is set at 400-600iu and adults’ at 600-800iu. 

If you feel that you need more than this, consult your doctor or nutritional therapist, who can assess your overall health and make the necessary recommendations.  

Julie Godfrey BSc (Hons) is a Nutritional Therapy Practitioner and full member of the British Association of Applied Nutrition and Nutritional Therapy (BANT). See or email


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