Vitamin D – how much do we need?

Today majority of the world’s population lives above latitude 35° N and is unable to synthesise vitamin D from sunlight for much of the time between late October and early April owing to the angle of the sun.

Vitamin D supplementation has been in the news a lot recently, here are just a few examples…

just a couple of days a go The Mail on Sunday carried an article by Roger Dobson called “Why levels of Vitamin D are lower in the north” You can read it here. Dobsone writes…

“Results show clear differences in Vitamin D status between the north and south and marked ethnic differences,’ says the study.
Adequate Vitamin D levels are vital for good health. It helps the body absorb calcium for stronger bones, and too little can lead to osteoporosis in adults and rickets in children.”

Then there was this article in the Times last year

Multiple sclerosis could be prevented through daily vitamin D supplements, scientists told The Times last night. The first causal link has been established between the “sunshine vitamin” and a gene that increases the risk of MS, raising the possibility that the debilitating auto-immune disease could be eradicated.

George Ebers, Professor of Clinical Neurology at the University of Oxford, claimed that there was hard evidence directly relating both genes and the environment to the origins of MS. His work suggests that vitamin D deficiency during pregnancy and childhood may increase the risk of a child developing the disease….

And this piece in the Independent in January

High levels of vitamin D cut risk of colon cancer: study

High levels of vitamin D are linked with a lower risk of colon cancer, according to a comparison of more than half a million Europeans, published online Friday by the British Medical Journal (BMJ). Patients with the highest levels of vitamin D in their blood had a nearly 40 percent lower risk of colorectal cancer compared to those with the lowest levels.

So with a lot of stories in the news recently about vitamin D, I thought it would be a good idea to do a quick summary of what we know already.

Vitamin D – a brief history

Rickets, is a softening and bending of bones in children, it reached epidemic proportions during the industrial revolution where before the importance of exposing children to sunlight was recognised, many of children that lived in the cities with sunless, narrow alleyways developed rickets. One autopsy study done in Boston during 1800s showed that more than 80 percent of children had rickets.

Rickets was first described in the 17th century by Francis Glisson who stated in 1650 that it had first appeared about 30 years before in the counties of Dorset and Somerset.[72] In 1857 John Snow (physician) suggested the rickets then widespread in Britain was being caused by the adulteration of bakers bread with alum. The role of diet in the development of rickets was determined by Edward Mellanby between 1918–1920.[10] In 1921 Elmer McCollum identified an anti-rachitic substance found in certain fats that could prevent rickets. Because the newly discovered substance was the fourth vitamin identified, it was called vitamin D (in fact it’s not a true vitamin). The 1928 Nobel Prize in Chemistry was awarded to Adolf Windaus, who discovered the steroid 7-dehydrocholesterol, the precursor of vitamin D.

Until the early 1980, doctors thought that vitamin D was only involved in calcium, phosphorus, and bone metabolism. The in a paper called  “do sunlight and vitamin D cut the likelihood of colon cancer ” Garland CF and Garland FC [7]  proposed that vitamin D is protective against colon cancer in areas where people were the least exposed to natural sunlight. Today more and more evidence suggests they were right and that vitamin D can help prevent many cancers including; colon, breast, lung, pancreatic, ovarian, and prostate cancer[6].

Who is most at risk

I guess this is where the recent Mail on Sunday article comes in. Vitamin D is naturally produced by the skin when exposed to sunlight and human beings evolved in equatorial Africa where they would have had year round sun. Our African ancestors absorbed higher doses of vitamin D living exposed in that environment. A single gene mutation that occurred around 50,000 years ago is responsible for the development of white skinned humans. White skin, which has less melanin, produces vitamin D from sunlight six times faster than dark skin. So white skinned people were able to migrate to higher latitudes, populate Europe, Asia, and North America, because they were able to make enough vitamin D to survive.

Today the majority of the world’s population lives above latitude 35° N and is unable to synthesise vitamin D from sunlight for much of the time between late October and early April owing to the angle of the sun. For example in London (52° N), from October to April UVB photons are blocked by the atmosphere so one’s skin cannot make vitamin D. Ad to this that people are often wrapped in hats, coats and gloves and so only a very small area of skin is exposed to the sun and the problem becomes much worse. Today due to concerns about skin cancer most glass filters out natural UVB radiation from sunlight that produces vitamin D, so you don’t generate vitamin D when sitting in your car or by a window at work or at home.

Of course the problem is much worse for many groups of people. The elderly and infirm for example often do not leave their homes for long periods of time, putting them at even greater risk. And as the resent study highlighted above shows people with darker skin are particularly at risk.

How much vitamin D do I need?

In many countries milk is fortified with vitamin D, however in the UK it is not. In the UK the only food that has to be fortified with vitamin D by law is margarine (to replicate the levels of vitamin D found in butter). However, a pint of US fortified milk only has around 230 IUs of vitamin D and so you would need to drink at least one pint every day to reach even the minimum recommended level and children and those over 70 would have to drink over 2 pints daily.

Typically we can produce 20,000 IUs of vitamin D in just 10 mins of midday summer sun. That’s the equivalent of 100 pints of milk and studies have shown that it is very difficult to overdose on on vitamin D. In healthy adults, it would take over 50,000 IU every day for several months before toxic levels were reached [1]. The LD50 of vitamin D in dogs (the dose that will kill half the animals) is 3,520,000 IU/kilogram. One study showed that you can safely take a 10,000 IU vitamin D supplement every day, month after month safely, with no evidence of adverse effect [4].

It is almost impossible to get enough vitamin D from food alone as the table below shows [3]:

Selected Food Sources of Vitamin D [30]

Food IUs per serving* Percent DV**
Cod liver oil, 1 tablespoon 1,360 340
Salmon (sockeye), cooked, 3 ounces 794 199
Mushrooms that have been exposed to ultraviolet light to increase vitamin D, 3 ounces (not yet commonly available) 400 100
Mackerel, cooked, 3 ounces 388 97
Tuna fish, canned in water, drained, 3 ounces 154 39
Milk, nonfat, reduced fat, and whole, vitamin D-fortified, 1 cup 115-124 29-31
Orange juice fortified with vitamin D, 1 cup (check product labels, as amount of added vitamin D varies) 100 25
Yogurt, fortified with 20% of the DV for vitamin D, 6 ounces (more heavily fortified yogurts provide more of the DV) 80 20
Margarine, fortified, 1 tablespoon 60 15
Sardines, canned in oil, drained, 2 sardines 46 12
Liver, beef, cooked, 3.5 ounces 46 12
Ready-to-eat cereal, fortified with 10% of the DV for vitamin D, 0.75-1 cup (more heavily fortified cereals might provide more of the DV) 40 10
Egg, 1 whole (vitamin D is found in yolk) 25 6
Cheese, Swiss, 1 ounce 6 2
*IUs = International Units.**DV = Daily Value. DVs were developed by the U.S. Food and Drug Administration to help consumers compare the nutrient contents of products within the context of a total diet. The DV for vitamin D is 400 IU for adults and children age 4 and older. Food labels, however, are not required to list vitamin D content unless a food has been fortified with this nutrient. Foods providing 20% or more of the DV are considered to be high sources of a nutrient.

These minimum levels are based primarily on preventing rickets and osteoporosis. Many recent studies have shown that in fact that higher levels of vitamin D can have significant health benefits.

Last week in the UK the Times carried this story:

Vitamin D better than vaccines at preventing flu, report claims

The risk of children suffering from flu can be halved if they take vitamin D, doctors in Japan have found. The finding has implications for flu epidemics since vitamin D, which is naturally produced by the human body when exposed to direct sunlight, has no significant side effects, costs little and can be several times more effective than anti-viral drugs or vaccine.

Only one in ten children, aged six to 15 years, taking the sunshine vitamin in a clinical trial came down with flu compared with one in five given a dummy tablet. Mitsuyoshi Urashima, the Japanese doctor who led the trial, told The Times that vitamin D was more effective than vaccines in preventing flu.

Vitamin D was found to be even more effective when the comparison left out children who were already given extra vitamin D by their parents, outside the trial. Taking the sunshine vitamin was then shown to reduce the risk of flue to a third of what it would otherwise be.

Altogether 354 children took part in the trial, which took place during the winter of 2008-09, before the swine flu epidemic. Vitamin D was found to protect against influenza A, which caused last year’s epidemic, but not against the less common influenza B.

You can read the full report that the Time’s article was based on here.

During this study the children took 1,200 IUs of vitamin D [2].  The official US government advise is that to enjoy optimal health we should keep up a vitamin D blood level of ≥50–99 ng/ml. And depending on which report you read, somewhere between 50% and 75% of Americans do not meet this level and that 90% of African-Americans and Hispanic-Americans are lacking in vitamin D. And remember these figures aren’t based on any notion of optimal levels that might protect against flu or cancer, they are based on minimum levels to prevent rickets and osteoporosis.

Here is the current UK guidelines on vitamin D [8].

  • Babies under one year: should have 200 units (5 micrograms) daily of vitamin D. Breastfed babies should be given vitamin drops (see breastfeeding section above). Babies fed by formula milk do not need vitamin drops, as this milk already contains vitamin D.
  • Children aged over one year: should have 280-400 units (7-10 micrograms) daily of vitamin D. This is usually given as vitamin drops or tablets. Babies fed by formula milk do not need vitamin drops, as this milk already contains vitamin D. But when weaned on to ordinary milk they should have supplements, as ordinary milk in the UK contains little vitamin D. (Note: some countries outside of the UK do add vitamins to ordinary milk.)
  • Adults: supplements of 400 units (10 micrograms) daily. However, people who get no sunshine, and the elderly, probably need more – approximately 800 units (20 micrograms) daily.

So if you live above latitude 35° N in the absence of sufficient sunlight for much of the year how much oral vitamin D should you take. Some doctors are recommending huge doses of 5,000 ID per day[6]. While doctors in India and Canada give people a once-yearly injection of 600,000 IU of vitamin D [5] . Daily, weekly, or monthly vitamin D tablets work just as well. I think as a starting point the levels in the Japanese study of 1200 IU during the winter months would be good advice and I can see no harm in going taking even higher doses if you have a cold or flu.


1. Vitamin D. The Merck Manuals Vitamin D

2. Urashima M, Segawa T, Okazaki M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. American Journal of Clinical Nutrition 2010; March 2010

3. Dietary Supplement Fact Sheet: Vitamin D. Health Professional Fact Sheet. Office of Dietary Supplements, National Institutes of Health

4. Am J Clin Nutr 1999;69:842–856.

5. MJA 2005;183:10–12

6. Dr Donald Miller (cardiac surgeon and Professor of Surgery at the University of Washington in Seattle). Vitamin D in a New Light

7. Do sunlight and vitamin D reduce the likelihood of colon cancer Garland CF and Garland FC

8. Vitamin D Deficiency, Patient UK


About thegymmonkey

I'm a fitness junkie,interested in injury rehab and get back into competition. View all posts by thegymmonkey

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