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How Much Vitamin D Do You Need?

In a list of the nutrients most fundamental to human health, vitamin D would appear close to the top.

  Beneath that simple name, however, lies some unexpected complexity. There are, in fact, five types of vitamin D, called, as you might expect, vitamins D1 to D5. They’re a group of related but distinct natural steroids: organic compounds with a biological effect. 

  All are fat-soluble, meaning they dissolve within the fats that circulate through our bloodstreams. The body can and does store vitamin D within fat deposits for later use if our diets don’t deliver enough or our exposure to sunlight falls below a certain level.

Vitamins are essential micronutrients, meaning that the body cannot generate these substances or adequate amounts of them from other organic materials, so they must be absorbed from the food we eat – with one exception: vitamin D3. Our bodies can generate D3 – chemically known as cholecalciferol – from cholesterol, itself a type of steroid. This occurs when the outer layer of our skin is exposed to sunlight. But depending upon where you live and your lifestyle this may not be enough.

What’s the value of vitamin D?


Vitamin D is used by the body to fuel multiple biological processes. These include:

  • The absorption of calcium from food.
  • Balancing blood levels of calcium and phosphate – ensuring healthy bone growth and preventing cramps and spasms in our muscles.
  • Bone mineralisation and growth: low levels of vitamin D can cause brittle, weak or misshapen bones. In children, this condition is known as rickets. In adults a distinction is made between osteomalacia (bone softening) and osteoporosis (bone weakening).
  • Reducing inflammation.
  • Modulating cell growth, antibodies and the immune system, nerve-muscle connections and the metabolisation of glucose.
  Vitamins D2 – known as ergocalciferol – and D3 play the most vital roles in human health.

Is there an optimum level?


Just how much vitamin D do you need? Certain levels of vitamin D are associated with better health outcomes, but those levels vary. Individuals differ in their vitamin D requirements: older people, for example, require higher levels than younger ones. And given the role of sunshine in generating vitamin D3 within our epidermis, the environment in which we live will inevitably affect how much vitamin D we need to obtain from our diets. The time of year, the weather, clothing and the latitude of our homes all affect the amount of sunshine we’re exposed to and consequently the amount of vitamin D available to our bodies.

  However, on average, a dietary intake of 400-800 international units, or IU, (10-20 micrograms per day) would be considered a healthy baseline by most doctors. This should translate into a blood level of 20-30 nanograms per mililitre (ng/ml). However, some studies have suggested this level is too low and such researchers favour 1200 – 1600 IU or more per day. Between 1,000 and 4,000 IU (25-100 micrograms) should be sufficient to ensure health in even the most vitamin D deficient individuals. 4,000 IU is the safe upper limit: you should not exceed this without medical advice.

  A vitamin D blood level of 12 ng/mL or less generally indicates a deficiency.

  Although few people develop rickets or other extreme symptoms, vitamin D deficiencies are remarkably widespread in the modern world: unhealthy diets are common and a lot of people don’t soak up as much sun as they need. A 2011 study suggested that no less than 42% of the US population may be vitamin D deficient.  

 The following demographic groups are most at risk:

  • Infants.
  • Older people, especially those over the age of 70. Postmenopausal women are especially prone to vitamin D deficiency. 
  • The inhabitants of more northerly nations, where the levels of sunlight fall during the winter months.
  • People with darker skin tones, who are less receptive to the effects of sunshine. According to the study cited above, vitamin D deficiencies affect a remarkable 82% of the African-American population of the United States, alongside 70% of the Hispanic population.
  People who fall into these groups should be consuming vitamin D at the upper end of the healthy levels recommended by doctors – as should anybody with an identified vitamin D deficiency, especially during the winter months.

How to get more vitamin D


There are three principal ways to increase your vitamin D levels.

Maximise your exposure to sunlight

  This does not necessarily mean sunbathing, although that can help. Simply getting out and about and being active in the fresh air will boost your skin’s exposure to sunlight, as well as, of course, providing healthy exercise. Naturally, your exposure to sunlight will be higher during the spring and summer months but the sun still shines (at least some of the time) in the winter. Sunlight is the single biggest source of vitamin D for most people

Optimise your diet

  Dietary sources of vitamin D are surprisingly limited when compared to other nutrients. The only vitamin D rich foods available to most people are: 

  • Oily fish such as sardine, mackerel, herring and salmon
  • Egg yolks
  • Liver
  • Red meat

Supplements and fortified foods

  Explore the health section of your local supermarket or the shelves of the nearest health food shop and you’ll find a multitude of dietary supplements, from the cheap and cheerful to top of the range brands with a price tag to match. Most people opt for broad spectrum multivitamin and mineral products – and these will all contain vitamin D to at least a healthy baseline level. But specialist vitamin D tablets are also available for those who wish to focus on this crucial nutrient.

  If you take one tablet a day with your breakfast you’ll enjoy the reassurance of having covered all the bases – you’ll be getting at least the minimum level of vitamin D needed for good health.

  But wait, there’s more. You may receive a further boost from some supermarket staples – most prominently breakfast cereals – which have been ‘fortified’ with vitamin D and other basic nutrients (typically vitamin B) during the manufacturing process. This is done to try and reduce the chances of malnutrition and ill-health amongst people who don’t eat a perfect diet and don’t take dietary supplements.

How to test your vitamin D levels

  So how do you go about checking your vitamin D levels? Unless you’re experiencing symptoms which clearly suggest malnutrition, your GP is unlikely to take much interest. But don’t be discouraged. It is quite possible to take a vitamin D test at home. 

These simple-to-use kits allow you to send in a small blood sample for full laboratory analysis. Once you receive your results, and learn just how much vitamin D is or isn’t circulating within your cells, you’ll be able to optimise your diet and fine-tune your health.

Sian Baker

Medically reviewed by Sian Baker, Dip ION mBANT mCNHC – Written by Beth Giddings.

Updated on 1st December 2021