Nov 30

Vitamin D and You

As winter draws in, there’s a lot of talk in the air about Vitamin D.  But what is it, where can you get it, and do you really need a supplement?  This article aims to take you closer to the answers to these questions, and more.

What is Vitamin D?

Vitamin D is a dietary component which is needed to maintain the right balance of calcium in the body.  This is obviously important for bone health, but could be a factor in heart health as well.  Vitamin D also regulates the levels of serotonin, the ‘happy hormone’, in the body, and may also help to regulate the expression of genes which regulate dopamine and noradrenaline, other hormones that play a role in mood.  This is why lack of Vitamin D has been linked to problems with mood and mental health.  The best quality evidence is found for the role of Vitamin D in bone health, although it’s likely that Vitamin D plays a role in many other areas of our wellbeing too.  Some studies have linked Vitamin D insufficiency to autoimmune conditions, food allergies, type 2 diabetes, some cancers, neurological disorders and dementia.  It’s thought that optimizing Vitamin D levels throughout Europe could cut healthcare costs by 16.7%.

Where can I find Vitamin D?

Sunlight is our principle source of Vitamin D, and spending time outside is good for health in so many ways.

Sunlight is our principle source of Vitamin D, and spending time outside is good for health in so many ways.

Our primary source of Vitamin D is sunlight, specifically sunlight which includes ultraviolet B radiation.  Due to the ozone layer, as well as the climate, sunlight in many parts of the world does not contain enough UVB light for our Vitamin D needs throughout the year.
In order to get enough Vitamin D, you need to expose your arms and legs to sunlight for 5-30 minutes between 10am and 3pm twice a week.  People with darker skin may need longer.  You should still practice sun safety and ensure you don’t burn.  This assumes that you have access to good-quality sunlight with sufficient UVB.  If not, it’s wise to consider diet and supplements as well.  Ideally, we make 90% of our vitamin D ourselves, and get 10% from elsewhere, but that’s not always possible.

Vitamin D and Diet

Fresh fish

Oily fish is one of the dietary sources of Vitamin D

Vitamin D is the only vitamin that can be both made in the body and eaten in the diet.  However, there aren’t many dietary sources.  The best-known is cod liver oil, which has been used successfully to treat rickets (the disease caused by Vitamin D deficiency), but Vitamin D can also be found in freshwater oily fish (e.g. mackerel, sardines) and some oily sea fish (tuna and salmon), as well as eggs, butter and cheese.  Some foods, such as certain margarines and cereals, are fortified with Vitamin D. The best vegan source of Vitamin D is wild, dark-coloured mushrooms.  Dark green leafy vegetables contain Vitamin D too, but not in the most useful form for the body.


Do you need Supplements?

During the winter months it’s unlikely that you’ll get sufficient Vitamin D from sunlight, and you may not enjoy the dietary sources regularly enough to keep your levels topped up.  There’s conflicting advice about whether you should supplement, but the following groups are still advised to supplement between October and April:
  • grandmother and baby

    Elderly people and children may need extra Vitamin D

    The elderly
  • Pregnant or breastfeeding women
  • Babies and children up to the age of 4
  • People with dark skin
  • People who do not spend much time outside
  • People who cover their entire body for religious or health reasons
If you’re not in one of these groups, you might want to consider testing to see whether a supplement would benefit you.  Your doctor can test once a year, but if you want to test more often (for example, to monitor how effective your diet or supplement changes have been) and your doctor isn’t able to help, you can buy a very reliable, affordable test that’s analysed in an NHS laboratory.  You can find more information here: https://betteryou.com/vitamin-d-testing-service.
Testing your Vitamin D levels will tell you if you're getting enough

Testing your Vitamin D levels will tell you if you’re getting enough

All you need is a spot of blood, so if, like me, you’re needle-phobic, this might be a better option for you than a blood draw at the GP, and it can be done in the comfort of your own home.
To avoid deficiency, your blood level of Vitamin D should be at least 75 nmol/L.  Often, practitioners like to see a level of 100-150 nmol/L, as this gives a margin for error; if your Vitamin D level should drop, you’re unlikely to become deficient before the balance can be redressed.
When choosing a supplement, you should always choose D3 (cholecalciferol) as opposed to D2.  This is the form that is most effective at improving overall Vitamin D status.  Furthermore, Vitamin D2 supplements tend to be less high quality.
If you’re a vegan, be aware that many quality Vitamin D3 supplements are not vegan-friendly, so choose with care.
Vitamin D can be one of the easiest supplements to take, as it doesn’t involve swallowing pills or capsules.  Instead it can be taken as drops, spray or, my personal favourite, tiny lemon-flavoured melt-in-the-mouth tablets.

Are you likely to lack Vitamin D?

There have been at least 13 studies done in the UK to assess the Vitamin D levels of the population.  Of the 13 studies, none suggested that the average person has enough Vitamin D.  Most suggested that we don’t have optimal levels, and one small study even suggested that many of us might be deficient.
How the body processes Vitamin D from food and sunlight

How the body processes Vitamin D from food and sunlight

Deficiency and Insufficiency

Deficiency of any nutrient occurs when the levels of that nutrient are so low over time that they cause a specific deficiency disease.  In the case of Vitamin D, the deficiency disease is rickets, characterised by weakened bones and malformed limbs.  Rickets had been eliminated in the UK by the late 1940s, but has started to return in the last decade.  Insufficiency is when levels of a nutrient are not low enough to cause a deficiency disease, but are low enough to have the potential to contribute to other problems linked to the nutrient, or to inhibit optimal health.  It is better to address insufficiency well before it becomes deficiency, as deficiency diseases are nasty!
A recent review examined nearly 200 studies from 44 countries involving 168,389 participants, mostly from the northern hemisphere.  It was found that 6.7% of the population were deficient in Vitamin D, while 88.1% of the population are insufficient according to the criteria of the Endocrine Society.  No wonder some people call Vitamin D insufficiency a pandemic!

Conversion Aversion

Confused about how much Vitamin D you need?  I was.  Part of the problem is that everyone seems to work in different units. The active form of Vitamin D is not actually measured in the blood.  Instead the circulating form (25-hydroxyvitamin D) is measured in nanomoles per litre (nmol/L).  In food and supplements Vitamins D2 and D3 are measured in either microgrammes or international units.  That’s why you won’t see any relationship between the numbers on your blood results and the amounts on your supplements.  But in case you’re trying to compare different brands of supplements or recommendations, or you want to use food as much as possible, here’s a handy conversion table.
Value in Microgrammes
Value in International Units
Possible food equivalent
Recommended Daily Allowance (RDA) – newborns-adolescents (1)
 110g salmon
Recommended Daily Allowance (RDA) – general population (2)
120g sardines
Recommended Daily Allowance (RDA) – over 70s (2)
 160g sardines
Safe Upper Daily Limit (2)
 3tbls cod liver oil (but don’t try this!)
 (1) American Academy of Paediatrics
(2) Institute of Medicine (UK)
So, how does this relate to blood levels?  In order to raise your blood level by 25nmol/L you would need to take 25 microgrammes or 1000 IU of Vitamin D a day for 3 months.  This assumes that your levels are below 100nmol/L.  If they are higher, you may need a higher dose of supplementation to maintain or raise your levels.
Should anyone avoid Vitamin D?
People with sarcoidosis can be particularly sensitive to Vitamin D, so should be cautious about higher doses and be carefully monitored.  Doctors can prescribe very high doses of Vitamin D if you have a deficiency (one friend is on 25,000 IU).  If you’re on this dose, please ensure that you’re monitored every 3 months, and don’t stay on it indefinitely; irreversible kidney damage has been reported from Vitamin D overdose over time.
Women walking & holding hands

Spending time in nature has many benefits, not least exposure to sunshine, which is needed for Vitamin D production

In summary:
  • Spend time outside when you can, but practice safe sun
  • Seek out foods with a Vitamin D content
  • Consider supplementing in the winter, particularly if you’re in a vulnerable group
  • Remember newborns; the current advice is to supplement within a few days of birth
  • If in doubt, test!


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