By medical nutritionist Dr Sarah Brewer, an expert in food, herbs and supplements
Public Health England recommends that everyone over the age of one year should take a daily supplement providing 10mcg vitamin D during autumn and winter. This is the minimum needed to prevent deficiency disease based on its role in calcium and phosphorus absorption to maintain healthy bones.
Recent headlines were misleading
A recent review of vitamin D published in the journal Lancet Diabetes and Endocrinology claimed that vitamin D supplements do not prevent bone fractures and the government should ditch its advice that everyone should take them throughout the winter months. This was startling, given that it pooled results from 81 randomised controlled trials, involving over 53,000 people.
But most of these trials lasted just one year or less, and taking a supplement for less than a year can’t be expected to magically strengthen bones that have thinned over many years. And in most cases, vitamin D was given alone, without calcium supplements. Vitamin D can’t enhance absorption of what isn’t there – if thinning bones are due to poor dietary calcium intakes than vitamin D alone can’t reduce fracture risk.
The biggest problem with this study, however, is that only 831 people out of the 53,537 people involved had a vitamin D deficiency in the first place. Yet we live in northern latitudes where we don’t get sufficient ultraviolet light exposure to make our own vitamin D during the cold months of the year. According to Public Health England, around one in five of the UK population has blood levels of vitamin D indicating risk of poor musculoskeletal health, and they stated in response to this study that their precautionary advice remains appropriate. If you aren’t taking a vitamin D supplement I urge you to consider this.
Vitamin D is vital for immunity
This study only looked at research involving muscle and bones, but vitamin D has many more important roles. Have you ever wondered why you get more respiratory infections during winter than in summer? While huddling together indoors helps germs spread more easily, falling vitamin D levels are also to blame for reduced protection.
Vitamin D is involved in the activation of immune cells that hunt and destroy invading viruses, bacteria and even fungi. Researchers have also found that vitamin D is involved in the production of antibiotic-like proteins, known as defensins, in the airways. It’s therefore not surprising that people who have low vitamin D levels – especially in winter – are more prone to colds, influenza, bronchitis and even pneumonia.
Data from 25 clinical trials involving around 11,000 patients from 14 countries, published in the BMJ, found that taking vitamin D supplements reduced the risk of acute respiratory infections by 12 percent. Those who were vitamin D deficient experienced the most benefit.
And for people with asthma, which is often exacerbated by respiratory infections, a Cochrane review assessed the evidence from nine trials involving over a thousand children and adults with asthma. Taking vitamin D reduced the rate of an exacerbation that needed treatment with oral corticosteroids by 37 percent, and decreased the risk of requiring an emergency department visit or hospitalisation by a massive 61 percent. The researchers concluded that taking vitamin D supplements is likely to reduce the risk of severe asthma exacerbations.
Diet should always come first, but unless you eat two servings of oily fish per week (also found in liver products, eggs, butter and fortified foods) and obtain vitamin D from sun exposure (not possible during the cold months of the year) then vitamin D supplements are advisable.
Public Health England advise a dose of 10mcg (400 IU) vitamin D for everyone. I believe that most adults would benefit from taking a higher dose of 25mcg (1,000 IU) per day, increasing to 50 mcg (2,000 IU) per day for those aged 50 and over, as your ability to make vitamin D in your skin declines with age.
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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