Vitamin D - the new supervitamin?

Over the last 10 years the full effects of vitamin D have just started to be understood. Until recently this vitamin has been badly overlooked, with the result that the recommended daily amounts and upper limits need to be increased to reflect the latest findings.

More importantly it appears that a lot of people are suffering from chronic diseases such as cancer, osteoporosis and heart disease that would be less likely if they had higher levels of vitamin D in their body.

Knowing how to raise our vitamin D status is something we all need to be aware of as most of us do not get enough for optimal health.

What does Vitamin D do for us?


  1. Maintains our calcium levels, preventing bones loss and keeping our nerves working properly, which leads to greater muscle strength.
  2. Helps cells develop properly and prevents proliferation of cells, reducing the risk of some types of cancer and the skin disease psoriasis.
  3. Prevents fibromyalgia (a generalised aching of the muscles), which is often a sign of vitamin D deficiency.
  4. Balances our immune system. It prevents overreactions that cause autoimmune disease and boosts innate immune defences, that reduce the chance of infections.
  5. Helps improve our blood glucose tolerance, improving symptoms such as mood swings, fatigue and reducing the chance of developing type II diabetes.
  6. Reduces blood pressure when it is caused by too much renin produced in the kidneys.

The list above shows that vitamin D is critical to our well being. If we don't get sufficient vitamin D then a long list of diseases are made more likely. Some of these diseases are very common. These include:

  • Osteoporosis (brittle bone disease) - the bane of many older people, especially affecting women in their 70s and beyond. See point 1 above, calcium levels need to be maintained at proper levels.
  • Cancer, especially of the breast (mostly women), prostate (men) and colon (both sexes). See point 2 above, excess proliferation of cells with mutations leads to cancer.
  • The skin disease psoriasis. See point 2 above, excess proliferation of some types of skin cell leads to psoriasis.
  • Fibromyalgia (generalised aching of our mucles). See point 3 above. Vitamin D also makes our muscles stronger.
  • Autoimmune diseases such as multiple sclerosis, rheumatoid arthritis, type I diabetes and inflammatory bowel diseases (Crohn's and colitis). See point 4 above.
  • Generalised infections, such as colds and flu, as vitamin D enhances our innate immunity by boosting our production of anti-bacterial proteins. See point 4 above.
  • Type II (adult-onset) diabetes. See point 5 above.
  • Hypertension (high blood pressure), which can increase the likelihood of heart disease and stroke. This is true when the hypertension is caused by an over active kidney. See point 6 above.

Where does vitamin D come from?

Technical bit:

Vitamin D, a type of steroid, comes in various forms which are numbered from 1 to 5. Vitamins D1, D4 and D5 you can safely forget about.

Vitamin D2 (ergocalciferol) is produced in some invertebrates and fungi when they are subjected to UV rays from the sun. Although this type of vitamin D is sometimes available as a supplement, you should not use it as it does not act in the same way as vitamin D3, and is associated with increased risk of death in epidemiological studies. Don't use it!

Vitamin D3  (cholecalciferol) pictured below the D2 is produced when UV rays from the sun hit cholesterol in our skin or in breast milk. It then is transported to the liver where it has a hydroxyl group (OH) added to it becoming calcidiol. This calcidiol is what is measured in our blood when we have our vitamin D levels tested. This is not the most active form of vitamin D however. For that to be produced, the calcidiol has to visit the kidneys or a large white blood cell found throughout our body called a macrophage. Here it is converted by the addition of another hydroxyl group (OH) into calcitriol. If your blood levels of vitamin D are low, then supplementing calcitriol is your best bet, although any form of vitamin D3 should be OK.

Less Technical bit:

Most of the vitamin D we receive is produced when UV rays from the sun hit cholesterol in our skin and produce vitamin D3. It follows that being out in the sun is something that will boost our vitamin D status. It is also available from our diet in the form of oily fish such as sardines, mackerel, tuna steaks, herrings, salmon and trout. Some fortified breakfast cereals, milk and butter also contain it. While oily fish are the best dietary source of vitamin D they do not compare to direct skin exposure to the sun. For instance 10 minutes exposure to direct sun in the summer can produce 10,000IU of vitamin D in just 10 minutes. To get that much vitamin D from your diet you would need to consume 2.5 kg of salmon and even more eggs, cheese and butter. Also as pointed out below, the vitamin D produced in the skin from sunlight lasts about twice as long in the blood as vitamin D from food sources.

So how do we know if we have enough vitamin D?

It has been estimated that at least 1.5 billion people worldwide are deficient in vitamin D. In the First World vitamin D deficiency was well known in the 19th century, with extensive epidemics of the bone disease, rickets in children. After the 2nd World War improved housing led to improved access to the outdoors. This, along with the clean air acts in the cities and fortification of some foods with vitamin D, helped to nearly eradicate rickets. Unfortunately, since the 1970s, dermatological societies and sun cream manufacturers along with Government, have discouraged exposure of the skin to the sun. The consequence has been the reappearence of rickets in our children with the chief medical officer rather belatedly calling for a review of recommendations this week1.

There are blood tests available starting from about £20 in the UK. Blood tests should measure levels of calcidiol, which is basically vitamin D after it has been converted by the liver, but before it is converted by the kidneys into its most active form, calcitriol. Some Doctors may try to order a calcitriol test, which is the form of vitamin D3 that has been activated by the kidneys, however this is not a good indicator of vitamin D status and can even be normal or high in people who are deficient in vitamin D. So if you get tested make sure it is a calcidiol (25 hydroxy vitamin D3) test, and not calcitriol (1,25 hydroxy vitamin D3). Note that your calcidiol levels will vary, typically by a factor of 2 through the seasons in temperate regions of the world like the UK and USA.

A good blood level for the calcidiol form of vitamin D is 125-150nmol/L (50-60ug/L).

How do we go about boosting our vitamin D status?

  • Getting direct skin exposure to UVB rays from the sun is the best idea.
  • Eating foods rich in vitamin D3 makes good sense, although it is not nearly so effective as getting UVB exposure.
  • Taking vitamin supplements could be worthwhile, especially if you know your blood serum levels are low.


The vast majority of articles whether online or in journals state that in Northern latitudes you can't get any vitamin D from UV rays between the months of September and March. Unfortunately the vast majority of "experts" are wrong on this. UVB rays don't know what month, it is and will reach your skin if nothing gets in the way. On a dark cloudy November day at 50 degrees north (Vancouver - Canada or Plymouth - UK), it is arguable that going outdoors won't get you much vitamin D. However if it is a sunny day, it will definitely be worth going outside. Add in snow or any other reflective environment such as open water and the rays will reflect back onto your skin adding to the amount that converts cholesterol to vitamin D3 in your skin. My rule is to use suncream or cover up only if I expect to get sunburnt. If you know this is unlikely just forget the suncream.


Vitamin D from foods lasts for between 1-2 weeks in our bloodstream, while vitamin D from the sun lasts between 2-3 weeks, which again emphasizes the importance of getting outdoors. However there is vitamin D available from some foods. The best are: oily fish and eggs.


People with fairer skin absorb more vitamin D and those with a naturally dark skin absorb less. If you live in high latitudes and have dark skin you may need to get more sun exposure or failing that, eat plenty of oily fish or take a vitamin D supplement. If you want to be sure before supplementing with vitamin D, then get a blood test done. However supplementation with anything up to 4,000IU (100ug) is approved as safe by the United States Institue of Medicine. There is however little evidence that doses up to 10,000IU (250ug) will be in any way harmful2. You will find most supplements come as 400IU, which is rather low if you do have low blood levels of vitamin D and want to boost them.