So, to what extent should you be considering the vitamin D levels of your clients? What’s the evidence for the vitamin’s involvement in reducing the risk of named medical conditions? And should you be worried about potential toxicity?
Most of us are well aware of the importance of vitamin D in bone health – and especially its ability to ward off the childhood bone disease rickets.
But did you know that vitamin D, (which, strictly speaking, is a steroid hormone), is involved in the expression of more than 1,000 genes (2)?This means it acts on cells in every organ of the body and has extremely farreaching effects on human health. Here are some of its key roles:
According to many experts, the answer is, ‘probably not’!
Vitamin D status is assessed by measuring serum levels of 25- hydroxyvitamin D (25(OH)D3. ‘Normal’ reference ranges vary but in the UK it is approximately 40-140nmol/L. In the US the Institute of Medicine has set the threshold at 50nmol/L(9) (see note at end of article.) However, many otherwise ‘healthy’ people who get their serum levels checked are surprised to find that they are only at the bottom end of this range.
Moreover, many doctors and scientists believe that 40nmol/L is far too low for good health and that the minimum level to aim for is 75nmol/L(10,11). One argument is that the reference ranges for serum 25(OH)D are set at the level observed in people who are considered ‘normal’ only because they do not have rickets; and that the prevention of longer-latency diseases, such as cancer, requires far higher serum levels(12,13).Some experts even believe that we should be looking to reach levels as high as 100-150nmol/L if we want to reduce the risk of chronic diseases(1,13, 14).
Given that the average serum level of vitamin D is estimated to be 54nmol/L(15), it is not surprising that so many experts are concerned about a global insufficiency(1,16, 17). It has even been proposed that if the worldwide average was increased to 105nmol/L, all-cause mortality would drop by 21%, life expectancy would increase by 2 years and healthcare costs could reduce by 20%(17).
If Heaney and others are correct and we are indeed low in vitamin D, why might this be the case? One reason could be that it is hard to get what we need from food. In the UK, the only significant food source is oily fish. Most of our vitamin D comes from the sun. The chart below shows how it is synthesized.
But there is a problem: many people in the UK never get what they need from sunlight alone because sunlight’s ability to help us produce vitamin D is hampered by season (it only works in the summer), latitude (the UK is pretty far north), time of day (needs to be between 11am and 3pm), cloud cover (complete cloud cover reduces vitamin D synthesis by 50%), smog/pollution (most of us live in cities), skin melanin content (the darker skinned you are, the less vitamin D you’ll get from the sun) and sunscreen (SPF of 8 and above).
Even in summer, when vitamin D is most available, it is estimated that 45% of the English population have vitamin D levels of less than 40nmol/L (deficient) and that 75% fail to reach the ‘optimal’ level of 75nmol/L. Levels are worse in winter; and worse in Scotland, where people are twice as likely as the Southern English to have low serum vitamin D levels and are far more likely to suffer chronic diseases(10,11).
This situation is causing such concern to some experts that they are calling for vitamin D deficiency to be classified as a major ‘lifestyle’ risk, like smoking, alcohol, obesity and being sedentary (10, 11).
And indeed, vitamin D insufficiency has been implicated in many different chronic diseases, such as:
In setting public policy on vitamin D, the UK and the US governments have focused primarily on bone health. They appear not to have take into account vitamin D’s many other roles, due to a lack of RCTs. (The RCT is the only study type that is generally considered to constitute true ‘evidence’. This, itself, is a cause for concern amongst advocates of integrative, person-centred healthcare.)
In the UK, there is no RNI for vitamin D, except for the elderly (400 iu or 10µg), babies (8.5µg) and young children (7µg) (33) Vitamin D testingis not usually undertaken unless there are exceptional circumstances, such as having a bone disease, being pregnant or breastfeeding, or being covered up or housebound for long periods. Moreover, The NHS advises caution with regard to sun exposure, (due to the risk of skin cancer), and vitamin D supplementation, (due to potential toxicity) (34) .
This type of guidance has been heavily criticized by doctors and scientists in the US and the UK (11, 17, 35) . They are concerned that it could lead GPs and patients to assume that, unless they fall into one of the special categories listed above, there is no need to be concerned about vitamin D status. How many of your clients, for example, are aware of the crucial importance of getting an adequate amount on a regular basis?
The concern around toxicity is due to the potential for hypercalcaemia at excessive vitamin D levels. However, recent studies have indicated that we would need to supplement extraordinarily high doses in order to reach the ‘toxic’ threshold. For example, a 2007 review of 15 human intervention trials showed that up to 10,000 iu/day is safe (36) and a 5-year 2011 study indicated that even a dose of 40,000 iu/day is unlikely to be toxic (37). The UK’s Expert Group on Vitamins and Minerals acknowledges that supplementing as much as 4000iu/day is unlikely to have any effect on blood calcium levels (33, 38).
In the US, public health messages stress that serum levels of more tan 125nmol/L can cause ‘adverse effects’ (9). However, critics claim that this cautious stance is based on the results of a study that used a single, annual mega-dose of 500,000 iu, which would have led to a sharp but transient rise in serum levels, followed, two months later, by ten months of pre-dosing (i.e. inadequate) levels (39, 40) . This is because the half-life of vitamin D is only 60 days. By implication, even if your clients are able to get enough vitamin D from sun exposure in the summer months, they are likely to be deficient in the winter unless they can obtain it from other sources.
So, should we supplement, and, if so, how much? Vitamin D supplements come in two forms: D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the natural form and is thus considered to be more bioavailable than D2. Most multi-vitamin supplements contain low enough levels (typically 200 to 400 iu) to take daily without issue but if you are going to prescribe therapeutic doses, the most sensible course of action would be to test serum levels first, preferably via the client’s GP.
If serum levels are found to be lower than optimal (75nmols/L as a base; 100-1 50nmols/L according to some experts), encourage more intake from food and sensible sun exposure. This means exposing skin daily, in the middle of the day, without sunscreen. Start with 2 to 3 minutes only, and build up gradually to a maximum of 30 minutes, taking care not to burn. Seven major UK health charities, including Cancer Research UK and Diabetes UK, have now developed a new joint position statement on vitamin D and sun exposure: ‘Enjoying the sun safely, while taking care not to burn, can help to provide the benefits of vitamin D without unduly raising the risk of skin cancer.’
If necessary, consider vitamin D supplementation at a level according to baseline serum levels, the skin type and the client’s diet and lifestyle going forward. The rate at which serum levels rise tends to vary between individuals. A re-test in 3 to 6 months will enable you to monitor and control the dose to the best effect.
Vitamin D has long been known as an important nutrient for skeletal health. But there is now emerging evidence that links vitamin D inadequacy with the development of many other long-term, chronic illnesses. There is still significant disagreement on the extent of vitamin D deficiency and the extent to which increasing levels may reduce the burden of chronic disease. We hope that this information on vitamin D has helped to explain some of the key issues surrounding vitamin D in human health and that it will help you in educating your clients, enabling them to make informed choices with regard to diet, lifestyle and supplementation.
Note: Some UK labs have now moved to µg/L, with values approx 25% of nmol/L values. To convert µg to nmol, multiply µg by 2.5
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