Vitamin D: A Powerful Health Boosting Vitamin and a Deficiency Pandemic


As a nutritionist, I am not a big supporter of lots of supplements in our diet and I believe that eating an unprocessed, whole foods diet with lots of variety will ensure most of us get all the nutrients we need for a healthy body and mind. However, there is one vitamin that I strongly recommend my clients to take as a supplement during the winter months where optimum levels of this vitamin cannot be achieved due to Ireland's latitude. For that reason, I want to give you a little information on this health-boosting vitamin, Vitamin D and let you decide if you feel supplementation in the months ahead would be good for you. It has long been recognized that people living at higher latitudes are at an increased risk of many chronic diseases including: different cancers, diabetes, cardiovascular disease, MS, rheumatoid arthritis, osteoarthritis, depression and Alzheimers’ disease among others (Holick, 2010). Evidence suggests that the rates of these diseases could be lowered significantly if we have adequate vitamin D levels (Holick, 2004). This raises the question: should we be prudent and avoid vitamin D deficiency to help us achieve optimum health and immunity?

Vitamin D plays a complex role in our bodies. It is quite unique in that it behaves more like a hormone than a vitamin. Its hormonal actions can influence almost every tissue in the body and that is why it is so important for our health and it plays a far more intricate role in the body than just protecting our bones.

Even if you eat relatively good sources such as oily fish, eggs, liver, meat and fortified foods you’re still going to fall short of optimum levels as diet typically provides less that 10% of our vitamin D requirements with more than 90% needed to come from exposure to the sun (Holick, 2004).

Studies have shown that just 10-20 minutes of safe summer sun exposure on at least a quarter of the body in a young white person can produce 1000IU of Vitamin D. If you have darker skin you may need longer than that to maintain optimal vitamin D levels. I would recommend keeping your face protected, as the skin is much thinner than other areas of the body and at a higher risk of damage, but aim to get at least a quarter of the rest of your body exposed for this short period of time when the sun is high.

That’s all fine during the summer months when the sun is shining and the temperatures are warm, however if you live somewhere like Ireland, high in the northern hemisphere, the correct UVB wavelength of sunlight for making vitamin D does not reach us between end of October and end of March, which makes it highly unlikely to sustain adequate vitamin D levels throughout winter without supplementation.

A study in the UK concluded that 47% of adults don’t even reach levels of 16ng/ml in the winter/spring season and 87% do not reach the desirable level of 32ng/ml. They noticed too that even in the summer months as much as 61% of people still failed to reach 32ng/ml, the desired levels of vitamin D (Hypponen, 2007).

Supplementation: How much do we need?

There are different views on the level of supplementation of vitamin D. However, it is suggested a recommended range of 20-32ng/ml of vitamin D should be maintained all year round for adults. With careful sun exposure this can be achieved in Ireland in the summer months. However, during the winter months when UVB rays are not available (due to our high latitude) how much vitamin D should we be taking?

An Irish study calculated to be confident that most adults (97.5%) maintain levels about 20ng/ml during winter a dose of 1,200UU per day is needed (Cashman, 2008) So it is recommended that 1,200IU should be taken as a daily supplement from the end of October until the end of March and safe sun exposure during the summer months.

It is worth noting that there are a number of factors that affect the production of vitamin D in the skin:

Age: As you get older, your body is less effective at converting the sun’s UVB radiation into vitamin D

Latitude: For those of us living in higher latitudes, the correct wavelength of UVB light to manufacture vitamin D does not reach us from mid October to the end of March

Skin Colour: The darker your skin colour, the more melanin you have which absorbs UVB so more time is needed in the sun to make vitamin D

Sunscreen: using sunblock as low as SPF 15 can reduce vitamin D production by 98%

Body fat: Vitamin D is taken up by fat cells which means less is in circulation

Skin exposure: greater skin exposure means great areas available for vitamin D synthesis.

Time of day: The higher the sun the more UVB rays reach the ground

Therefore to maximize health and reduce the risk of many chronic diseases it is not a bad idea to keep an eye on your 25(OH)D (measurement of vitamin D) blood concentration (just as most of us watch the cholesterol levels). The only way to be sure you are supplementing with the right amount for your body is to have your blood levels tested by your doctor on your annual check up to ensure you are keeping it within an optimal, healthy range.


Cashman, K.D., Hill, T. R., Lucey, A. J., Taylor, N., Seamans, K. M., Muldowney, S., et al. Am J Clin Nutr., 2008: 88(6): 1535-42

Holick, M.F., (2004) Sunlight and vitamin D for bone health and prevention of autoimmune diseases, cancers, and cardiovascular disease. The American Journal of Clinical Nutrition. 80(6) 1678S-1688S

Holick, M.F., (2010) The Vitamin D Deficiency Pandemic: a Forgotten Hormone Important for Health. The Public Health Reviews. 32(1), 267-283

Hypponen, E., Power, C., (2007) Hypovitaminosis D in British adults at age 45 y: nationwide cohort study of dietary and lifestyle predictors. The American Journal of Clinical Nutrition. 85(3): 860-8.