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Vitamin D - the Sunshine Vitamin

Updated: Mar 5, 2021

Vitamin D is known as the Sunshine Vitamin; synthesised in the sebaceous glands of the skin by the action of sunlight. In 2016, the Scientific Advisory Committee on Nutrition (SACN) reported that around 30-40% of the population had lower levels of Vitamin D in Winter, compared to 2-13% in the Summer months. In the UK we can synthesise Vitamin D from sunlight between April and September and store some for the Winter months however, the levels depend on factors such as skin colour, time spent in the sun, age and location - leaving some people at risk of deficiency all year round.

The most at risk groups are those that lack sunlight exposure in the Summer months such as institutionalised adults or those that work indoors for the majority of the day.The elderly are also at risk as vitamin D as manufacture in the skin becomes less effective with age, with reductions up to 75%; therefore, those in care homes or hospital stays are particularly at risk. Those with darker skin have a reduced efficiency to absorb UV light, making them especially vulnerable when living in colder climates.

Vitamin D3 is found in some foods such as dairy, organ meat and oily fish. D2 is found in vegan foods such as mushrooms and almond milk; D3 is more readily converted than vitamin D2 and it can therefore be difficult for those following a vegan diet to keep their levels sufficient, especially during Wintertime. Studies show that low levels of vitamin D were found to be more prevalent in those following a vegan diet compared to those following an omnivore dietary approach, with 73% versus 46%, respectively. In any of the above cases it is worth asking for your Vitamin D levels to be checked by the doctor.

In July 2020, Public Health England met with the SACN (the government's health advisors) and an increase in the recommended daily allowance for Vitamin D from the original requirements [set out in 1991 and 2016] were recommended. An increase of 10mcg (400iu) has been set to ensure a minimum blood level of 25ng/mL can be maintained all year round. Worryingly, in the UK, average blood levels are just 19ng/ml and therefore intake has been increased.

Many health experts believe our requirements should be set much higher, including the Vitamin D Council, the Endocrine Society and Grassroots Health. Grassroots Health, a cohort of independent Vitamin D researchers, suggest our levels should be around 4-6 times higher than that recommended by the SACN. 30 ng/ml of blood calcium is deemed to be satisfactory but levels of 40 - 60 ng/ml are considered effective for immunity and optimal health. But why are health experts recommending higher intakes of vitamin D?

Vitamin D is perhaps most well-known for preserving bone integrity and protection from osteoporosis and rickets but researchers have found that Vitamin D regulates many more physiological functions. Low levels of Vitamin D may play a role in cognitive dysfunction, muscle weakness, fatigue, diabetes, cardiovascular disease, autoimmune diseases and frequent susceptibility to bacterial and viral infections.

Low levels of Vitamin D have been associated with a risk of high blood pressure; while the exact mechanisms remain unknown it is likely Vitamin D reduces inflammation associated with heart disease. Elderly with low levels of Vitamin D were found to be twice as likely to develop dementia compared to those with normal levels; again the exact role is unknown but it is likely that Vitamin D protects nerve growth. Vitamin D is also needed for the neurotransmitter acetylcholine, which is a chemical involved in memory; in rats a decline in memory and learning was improved with Vitamin D supplementation.

Evidence from around the world shows that in areas where sun exposure is low there are increased cases of MS, inflammatory bowel disease and rheumatoid arthritis, pointing to the anti-inflammatory and immune modulating effects of vitamin D. In the case of diabetes, the secretion of insulin by pancreatic beta cells, may be impaired if there is a lack of vitamin D; with the Vitamin D Council suggesting that “people with high vitamin D intake during their first year of life are less likely to develop type 1 diabetes later in life.” Why obesity? Research is still vague but it is suggested those with obesity may need higher levels than those of normal weights.

Vitamin D has attracted much attention in our current health climate due to its role in the immune system. During COVID-19, it was found that there was a higher number of mortalities within the non-white communities; as well those suffering from obesity, diabetes, cardiovascular disease and the elderly - all those in risk categories for low levels of Vitamin D, or symptoms thereof.

It is estimated non-white skinned populations could be around 55-60% deficient in Vitamin D, compared to those of white-skin at around 20% of their population and perhaps why COVID-19 has affected this group particularly. The UK and Belgium have the highest levels of vitamin D deficiency and highest number of deaths suggesting that vitamin D levels may play a part in our susceptibility to COVID-19.

But what about those countries with low levels of sunlight such as the Scandinavian countries? Their levels in general are higher despite their latitude due to widespread awareness of Seasonal Affective Disorder, to which vitamin D can benefit this depressive disorder. Furthermore, many foods are fortified as well as high consumption of oily fish which contains Vitamin D; in comparison in the UK where we tend to opt for lower fat diets and few foods are fortified with Vitamin D. Interestingly, air pollution has been suggest as a possible cause to the outbreaks in China and Northern Italy as sunlight (UVB) is blocked by air pollution and therefore producing reduced Vitamin D stores in the population.

A preliminary Indonesian study looked at 780 people found to be SARS-CoV-2 positive. It was found that 4% of patients with 30ng/ml blood levels of vitamin D died, compared to a 87.8% and 98.9% death rate in the groups 20-30ng/ml and less than 20ng/ml, respectively. The death rate was therefore found to be 7.63 and 10.12 times as likely in the insufficient group and deficient group, respectively. Men were found to be worse affected compared to women. Interestingly, men may be more susceptible to infection as our innate immunity genes are found on the female chromosome, women therefore having two copies and it is thought that the interaction of these genes may result in lowered immunity.

Viruses and Flus happen in the Winter months but not necessarily because they dislike heat but rather due to our increased susceptibility where are blood levels of Vitamin D are lower. Let’s briefly take a look into how vitamin D and why researchers suggest vitamin D has the potential to reduce susceptibly to COVID-19.

The sebaceous glands in the skin produce 7- Dehydrocholesterol, a molecule made from cholesterol, which when exposed to sunlight is converted to cholecalciferol (Vitamin D3). D3 is then transported to the liver where it is converted to Calcidiol (25- hydroxy-vitamin D); before being finally converted to its biologically active form called Calcitriol (1,25 hydroxy-vitamin D). Our cells have Vitamin D Receptors (VDRs)on them which instruct our DNA to make a functional product, especially found in the cells of the immune system and white cells which fight infection. They are also found in our respiratory epithelial cells which line our lungs and gut - our areas of defence from the outside world. Calcitriol acts as a hormone which increases the expression of VDRs. When foreign invaders such as bacteria and viruses enter our body these instructions are increased and the skin junctions tighten reducing the passage of invaders. It is perhaps easy to see how we can be susceptible if our levels are low.

When blood pressure drops for any reason, kidney cells release renin into the bloodstream which causes a series of conversions; essentially our thirst mechanism is stimulated and angiotensin II is produced. This causes an increase in water volume and therefore pressure and construction of our blood vessels and associated with increased inflammation. Vitamin D blocks the production of renin and therefore reduces the amount of angiotensin II and potential excess inflammation.

Within the same chain, is an enzyme that also keeps inflammation in check, Angiotensin Converting Enzyme II (ACE2); studies suggest lowered Angiotensin Converting Enzyme II results in cardiovascular disease and lung injury. Angiotensin converting enzyme II is a zinc containing enzyme found in membranes in the lung, gut, heart and vessels. Vitamin D up regulates this enzyme. COVID-19 enters the body by this receptor and infection causes this enzyme to reduce; when combined with low levels of vitamin inflammation could ensue and the virus to take hold.

Vitamin D is also needed for the response of the innate immune system - the first line of defence by enhancing antimicrobial activity which happens in just a few hours. Compare this to our adaptive immune system which makes antibodies against an invader but can take days to get a response. Children have a less strong adaptive immune system and a great innate - perhaps a reason why COVID-19 affects them less strongly.

Interestingly, as I suffer from my own blood disorder I have researched significantly into anticoagulants. A number of studies suggest that Vitamin D has anticoagulant properties and there are links that low levels can lead to DVT and suppresses inflammatory cascades in the body; many of the complications of COVID-19 involve blood clots which impede airways and optimal levels of Vitamin D may reduce additional complications.

In 2102 the Institute of Medicine report indicated that 10,000 IU/day is considered the maximum NOAEL (no observed adverse effect level). Studies suggest around 6,000-10,000 IU per day are required to maintain optimal blood levels of 40ng/ml levels however 4000 IU/day is considered a safe intake level for adults. Grassroots Health suggests not taking more than 4000 iu per day of during the Winter months for a maximum of three months, reducing to recommended levels in Summer months, levels should be tested after 3-6 months.

It is also important to consider that nutrients that work in synergy within the body. Magnesium is required for the conversion of vitamin D to its active form and something many of us are also deficient in. Vitamin K is also vital to keep calcium out of the arteries and rather in bone where it should be; both of which can be found in plant foods and we should be aiming to eat 8-12 portions of vegetables and fruit each day; which also provide valuable antioxidants. Vitamin D enhances the expression of antioxidants, such as selenium and Vitamin C; if you read my last post on antioxidants you will know they stop damage and help to repair the body so another great reason to be including lots of coloured vegetables in our diet. Vitamin A must also be adequate which can be found in organ meat and orange vegetables. Zinc found in ACE2 should be supplied which is found in beef, shellfish and legumes.

It is also important to mention some cautions. You should always speak to your doctor before taking supplements to be safe and have your levels checked, especially if you have a pre-diagnosed disease as supplementation could be dangerous. Vitamin D increases calcium absorption so you should not take calcium supplements at the same time. It is vital to use common sense if considering vitamin D supplementation during Winter as excessive levels can also pose a risk to health so always be moderate and seek advice.

In the UK, sitting in the sun for 15 minutes in Summer, three times a week in t-shirt and shorts obtained less than 20 ng/ml of blood calcium - less than the minimum required amount. Wearing a bathing suit for 20-25 minutes of sun exposure in high summer during the hours of 11am-2pm provided optimal amounts. It is important to cover the skin before it burns; whilst studies suggest a moderate sunlight exposure without burning the skin outweigh the risks of cancers it is important to be responsible.

Free supplements containing vitamin D are available for children for low-income families. Please speak to your doctor or visit here:

So some very interesting research! I am a big believer in susceptibly to disease and the importance of nutrition being the best that we can offer our immune system. There are probably many factors to disease and each essential nutrient is vital to the body and has many roles, but, if having optimal Vitamin D levels help to reduce susceptibly as research suggests then this is a step in the right direction.

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