7 minute read

The saying goes that every cloud has a silver lining: for me, there’s been several silver linings in the pandemic cloud, notably working from home, being with my dog, and the shifting of the public spotlight onto vitamin D.

Acknowledged to play an important role in bone and muscle health, vitamin D has been drawing attention recently because of its possible role in the body’s immune response to respiratory viruses (hello, COVID-19). This Bitesize piece summarises relevant information about this micronutrient, offers guidance on whether you need to take a supplement and, most importantly, what type and at what dose. It will also tell you the single most important consideration in your thinking about vitamin D.

This information only applies if you are generally well; if you have specific health conditions affecting gastrointestinal function, nutrient absorption, or if you are using certain medications (particularly blood thinners or anti-coagulants), your multi-disciplinary care team will make appropriate recommendations.

Vitamin D and health: a quick summary. Vitamin D is a key micronutrient in any overall wellbeing strategy, including those that focus on supporting effective immune processes. We can get vitamin D from one of two routes: the food we eat (digest, and absorb), or we can make it ourselves by exposing our skin to sunlight; that’s why it’s referred to as the ‘sunshine vitamin’. Whilst skin synthesis is the major source of vitamin D for most people, it can also be obtained from the diet.

Nearly all dietary sources of vitamin D are animal- or fish- based. Foods such as oily fish (wild salmon, mackerel, sardines, pilchards, trout, herring and kippers are all good sources); mushrooms (Shi-itake in particular), egg yolk, milk, and certain fortified foods (though these tend to be heavily processed with additional salt and sugar) are usually recommended. Grass-fed beef liver and cod liver oil may be useful sources but may not be recommended for certain people including pregnant women.

For most people, dietary provision of vitamin D is insufficient to meet the body’s needs so reliance on skin synthesis increases. The changing nature of UK summers, when sunshine cannot be guaranteed or when sunscreen use prevents skin exposure, may affect many people’s opportunity for skin synthesis of vitamin D. Those who are housebound, or older, or who for cultural reasons keep their skin covered are particularly at risk. During the first lockdown of the pandemic, many of us had to stay inside and so may also be at risk of vitamin D deficiency.

As it plays a central role in bone and muscle health, vitamin D deficiency is linked to the development of rickets and osteomalacia. Whilst I’m not going to go into detail here about specific signs and symptoms that may indicate a potential vitamin D deficiency, given that every cell in the body has a receptor for (the active form of) vitamin D, it’s not surprising that low levels of this vitamin may play a role in many other health concerns, including the impairment of immune system function.

If our immune system isn’t functioning as well as it could, we could be more susceptible to respiratory viruses such as COVID-19. Vitamin D deficiency has been thought to play a part in the dramatic immune system over-reaction, called a “cytokine storm” experienced by some who contract the virus. This hypothesis, for it remains scientifically unproven at present, has in part developed because the groups at most risk of severe COVID-19 are the same as those at highest risk for severe vitamin D deficiency. The thinking is supported further by the geographical spread reflecting global higher population rates of vitamin D deficiency. You can read more here.

With many of us at risk of vitamin D deficiency, it’s reassuring that Public Health England (PHE) recently updated their guidance to state that, from October to March, everyone should be taking a vitamin D supplement; people who get little skin exposure to sunlight may benefit from including a supplement year-round. The supplement should provide 10mcg (400iu) of vitamin D. There’s more detail in the PHE guidance here.

Although there’s no evidence to support vitamin D supplements specifically to prevent or treat COVID-19, the UK government has advised that, in line with PHE guidance, during the pandemic everyone consider taking a supplement. This advice is based on the NICE Evidence review from June 2020; you can find that here.

Government guidance asserts that, for most people, the recommended dose of 10mcg (400iu) is considered to be enough, with an upper limit of 100mcg (4000iu). Whilst some people may require higher, therapeutic, doses, it’s definitely a case of “more is not necessarily better”: too much vitamin D may lead to a variety of signs and symptoms of health issues, including high circulating levels of calcium, in part because of its intricate relationship with so many vitamins and minerals.

Both ergocalciferol (D2) and cholecalciferol (D3) are approved for use; as a nutritional therapist, I recommend supplementing with the D3 form. There is plenty of supplements available, whether tablet, spray or drops, so there’s something to suit everyone. Whichever form is used, because vitamin D is fat-soluble, it should be taken with food containing an element of fat to encourage its absorption.

The single most important thing to do: Okay, you’ve stayed with me to this point: thank you, here it is.

The single most important thing to do before you decide to supplement is to consider your health status.

Your health status is important not only for understanding the type of supplement but also establishing the correct dose.

There are so many different brands and formulations of vitamin D supplements, often including accessory micronutrients such as calcium, vitamin K2, or magnesium, with different dosing regimens. By understanding any co-existing health concerns and goals, the ideal combination for you may be identified.

A review of health status may also indicate whether you may be at risk of deficiency that merits a supplement dose higher than that recommended by PHE.

If that’s so, then the next most important thing to do is test.

Many nutrition professionals, including me, recommend testing vitamin D levels before spring and after summer. This can reveal whether our winter strategy has been effective, offer guidance for the brighter months, and then review requirements for the coming winter,

Testing is simple and straightforward. I’d like to say it’s painless but we all have different pain thresholds and relationships with needles. So, simple and straightforward it is. Testing measures levels of the active metabolite, 25 hydroxyvitamin D (or 25(OH)D for short), in blood. This test may be available from your GP though services may be affected by the pandemic.

Other tests are available privately, and cost-effectively. They all measure 25(OH)D but use dried blood spot samples, obtained by pricking the side of a finger with a lancet rather than requiring a full blood draw. This may reduce any qualms rooted in needles. The lab I currently recommend is City Assays, part of the NHS and based in the West Midlands. They offer a competitively priced, dried blood spot, test with a report that’s easy to interpret and that will indicate if a therapeutic dose of Vitamin D is required. If you need a higher dose, consult your healthcare practitioner, pharmacist, or nutrition professional (ah-hem) for guidance. The test is easy to perform at home, with clear instructions and a lovely video on YouTube.

Once your health status has been reviewed, and the ideal product and dose identified, you’re “good to go” for a few months until a re-test can indicate the next steps.

So, in a nutshell:

  • vitamin D is the supplement of the moment, and for good reason
  • most of us may benefit from taking a supplement of D3 at 10mcg (400iu) every day; take it with food containing an element of fat
  • review your health status and goals before deciding which supplement to take
  • if you have signs and symptoms that suggest a greater need, check your vitamin D levels by testing
  • if your test result indicates a therapeutic dose is required, speak to your healthcare provider to agree the amount and have a re-test 3-6 months later to assess next steps

And remember: if you would like to have a quick (free) chat about this, or if you’d like me to review your health status and create your vitamin D strategy with you, I’m here. You only have to ask.

Stay well.

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