By medical nutritionist Dr Sarah Brewer, an expert in food, herbs and supplements

Not that long ago, vitamin D was all about calcium absorption and maintaining strong bones. Researchers now realise that, as a hormone, it has many other vital functions in the body, including supporting immunity, circulatory, heart, brain and joint health.

Why you may need a supplement
You can make vitamin D in your skin when the UV index is greater than 3. As a result, vitamin D levels tend to plummet during autumn and winter in people living in northern latitudes such as the UK. Even when the sun is shining, many people also fail to synthesis sufficient vitamin D because they cover up, use high SPF sunscreens, or stay in the sun for more than 20 minutes which causes inflammation (sunburn) that breaks down the vitamin D they’ve already produced.

Food sources then become important, but if you don’t eat much oily fish, liver products, eggs, butter or fortified foods, you are likely to remain deficient during winter.

Public Health England have found that 23% of adults aged 19 to 64 years, 21% of adults aged 65 years and above and 22% of children aged 11 to 18 years have low blood levels of vitamin D. They have therefore advised that everyone should consider taking a supplement supplying 10 micrograms vitamin D per day during autumn and winter months. This is the minimum needed to prevent vitamin D deficiency conditions such as muscle and bone aches and pains, osteomalacia or rickets. For optimum health, there is increasing evidence that higher doses of 25mcg to 50mcg vitamin D are needed, especially for older people as the ability to synthesise vitamin D declines in later life.

Health benefits of vitamin D 
Osteoporosis: The best known role for vitamin D is in regulating calcium absorption and its deposition in bone. Studies involving almost 64,000 people aged 50 or over suggests that taking vitamin D plus calcium supplements can reduce the risk of bone fracture by 12% to 24%.

Osteoarthritis: People with low vitamin D intakes are three to four times more likely to experience osteoarthritis progression than people with high intakes.

Diabetes: Data from 21 studies, involving over 76,000 people, showed that those with the highest vitamin D levels were 62% less likely to develop type 2 diabetes than those with the lowest levels. It’s thought that vitamin D improves insulin sensitivity to better regulate glucose control.

Heart disease: Vitamin D regulates calcium movements to help reduce the amount of calcium that accumulates in artery walls and also improves blood pressure control. Research involving 15,000 adults found that people with good vitamin D levels were 30% less likely to develop high blood pressure and 98% less likely to have type 2 diabetes.

Stroke: Data from 10 studies, involving over 58,000 people confirm that poor vitamin D status increases the risk of stroke. Those with the highest levels were up to 82% less likely to have a haemorrhagic stroke than those with low levels.

Breast cancer: A large analysis of data from 14 studies, involving over 25,000 women, suggests that every 10 ng/mL increase in blood vitamin D concentration is associated with a significant 3.2% reduced risk of developing breast cancer.

Brain: Results from 14 studies, involving almost 31,500 people, show that those with the lowest vitamin D levels are up to twice as likely to develop depression as those with highest levels.  Low levels of vitamin D are also linked with long-term (chronic) pain and increase the amount of narcotic analgesia needed for pain-relief.

Asthma: Adding oral vitamin D supplements to usual asthma treatment can reduce the risk of experiencing at least one severe asthma attack requiring hospital admission or emergency department attendance by over half, and reduce the need for rescue therapy with oral steroids by 37%.

Vitamin D may help you live longer
All in all, it’s not surprising that studies carried out in eight countries, involving over 26,000 adults aged 50 plus, found that those with the highest vitamin D levels were 57% less likely to die from any medical cause during the study duration than those with the lowest levels. Despite vitamin D3 levels varying with country, sex and season, the association between those with the lowest and those with the highest vitamin D level within each country was remarkably consistent.

How much do you need?
The EU RDA is 5 mcg (200 IU) per day but that is based on old understandings relating to calcium. A daily intake of 10 mcg (400 IU) to 25 mcg (1000 IU) is usually needed to maintain a healthy blood levels of vitamin D during winter months. The dose you need increases with age.

Look for supplements supplying vitamin D3 (cholecalciferol) as this is more effective in maintaining blood vitamin D levels than the vitamin D2 (ergocalciferol) form.

Safety
The European Food Safety Authority recently suggested a tolerable upper intake level of 100mcg per day (4000 IU) and this intake should not be exceeded except under medical supervision. Excess can lead to side effects associated with high calcium levels, such as demineralisation of bone, kidney stones, headache and weakness.

About Dr Sarah Brewer
Dr Sarah Brewer is a medical nutritionist and an expert in food, herbs and supplements. She qualified from Cambridge University with degrees in Natural Sciences, Medicine and Surgery. After working in general practice, she gained a Master’s degree in Nutritional Medicine. Sarah is a licensed medical doctor, a registered nutritionist and a registered nutritional therapist.

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For more information visit Dr Sarah Brewer’s Nutritional Medicine website at www.DrSarahBrewer.com and follow Dr Sarah’s tweets on nutrition @DrSarahB and general health @DrSarahBHealthy.