Vitamin D: The Sunshine Vitamin

Posted by on Sep 4, 2012 in Health, Nutrition, Supplements | 0 comments

Vitamin D: The Sunshine Vitamin

Vitamin D, in the true sense, is actually a hormone, not a vitamin. The human body can synthesis vitamin D as long as we are exposed to enough sunlight. This is why vitamin D is know as the ‘sunshine vitamin”. We can also get it through specific foods in our diet and supplements. When UVB rays from the sun hit our skin, an inactive form of vitamin D is produced.  This inactive form then travels to the kidney where it is converted to the active form, known as 1,25-dihydroxyvitamin D, which the body can use for many purposes.

Health Risks of Vitamin D Deficiency

Researchers have discovered that there are vitamin D receptors in all tissues in the human body including, the heart, brain, muscle and intestines, meaning these tissues need vitamin D to function properly.

We used to think that the only role of vitamin D was to regulate blood levels of phosphorus and calcium, keeping our bones strong and healthy but over the past several years, researches have discovered that this hormone plays a much bigger role than just bone health. They now know that the sunshine vitamin plays an important role in our immune system, creating a resistance to chronic diseases such as colon cancer, cardiovascular disease, obesity, diabetes, depression and Alzheimer’s (1).

In addition, low levels have shown to be a risk factor for cognitive decline in the elderly. One study looked at 6,257 elderly women and found that the women with low vitamin D levels, 25 (OH)D, had increased risk of cognitive impairment (2). Cognitive impairment is not the only effect vitamin D has on the elderly. It appears that maintaining normal serum levels of 25(OH)D can lower mortality in the general elderly population (3).

Low vitamin D levels are also affecting children. Researchers at the University of Michigan found that children who are deficient in vitamin D accumulate more abdominal fat than children who get enough vitamin D. It is well documented that increased abdominal fat is a risk factor for type II diabetes.

Causes of Vitamin D Deficiency

If this vitamin is so easy to obtain from sunlight, diet and supplements then why is it estimated that one billion people worldwide are deficient or insufficient in vitamin D? The answer is still unknown. Some researchers suggest the fear of skin cancer is causing people to limit their exposure to sunlight by avoiding the sun or using sunblock, which prevents vitamin D production or that our lifestyles have evolved to be indoors more often. Ethnicity plays a role as well. The darker the person’s skin color, the more sun exposure they need to obtain vitamin D from the sun. In the United States, African Americans have lower serum levels of 1, 25-dihydroxyvitamin D than Caucasians.

In addition, there are limited foods that contain naturally occurring vitamin D, mainly wild-caught oily fish (salmon, mackerel, bluefish, and canned tuna) and egg yolks. There are also fortified foods such as milk, baby formula, cereal and orange juice. If these foods are not consumed on a regular basis, levels could drop but experts claim that 90 percent of our vitamin D comes from sun exposure alone (4). 

Symptoms of Vitamin D Deficiency

Bone pain and muscle weakness can be a sign of vitamin D deficiency but the symptoms are often unnoticeable until symptoms of a complication are present (5).

Know your vitamin D levels

Now that we know the importance of maintaining optimal vitamin D levels how do we find out our own levels? Fortunately, there is an easy blood test that your physician can order in addition to your routine blood tests. There are typically two tests that can be ordered by your doctor. Below is an explanation of each.

1. Calcidiol (25-hydroxyvitamin D or 25(OH)D). This is the body’s main storage form of vitamin D. This will determine your vitamin D status.

2. Calcitriol (1,25-dihydroxyvitamin D or 1,25(OH)2D3). This is the activated form of vitamin D that is produced in the kidneys but serum levels of this form is not a good indicator of vitamin D deficiency (6).

Vitamin D sources

The best way to get vitamin D is through the sun. We absorb large amounts of vitamin D in a short amount of time when exposed to UVB rays. There are many factors that effect how much D we can produce from UVB rays, including the time of day, latitude, time of year, skin type and age. Someone above 60 years of age requires four times more exposure than someone in their 20’s.

There are also vitamin D supplements. The amount of vitamin D necessary to raise levels from deficiency to a normal range is very controversial and many experts have varying opinions. Again, there are many factors that come in to play such as age, weight, sun exposure, other heath conditions, medications and the quality of the supplement. When choosing a supplement, seek advice from a registered dietitian of other health care practitioner.

What works for one person may not work for another. The only way to tell if the regiment is working is to have the levels measured and then occasionally monitor.



  2. Slinin Y, Paudel M : Association Between Serum 25(OH) Vitamin D and the Risk of Cognitive Decline in Older Women. J Gerontol A Biol Sci Med Sci. 2012; gls075v1-gls075.
  3. Schöttker B, Ball D, Gellert C, Brenner H: Serum 25-hydroxyvitamin D levels and overall mortality. A systematic review and meta-analysis of prospective cohort studies. Ageing Res Rev. 2012 Feb; [Epub ahead of print]
  4. Holick MF, Chen TC, Lu Z, Sauter E.Vitamin D and Skin Physioology: a D-lightful story. J Bone Miner Res. 2007 Dec;22 Suppl 2:V28-33.

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