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9 Things You Need To Know About Vitamin D

It's essential for our health, yet there is so much about it that remains a mystery.

Vitamin D aka the "sunshine vitamin" is in the spotlight. It has been for years – research after research has shown that low levels of it is associated with everything from heart disease, diabetes, cancer, mood disorders to dementia. Most recently, it's been promoted as a potential defence against the coronavirus (the jury is still out, so please, wear your mask and take necessary precautions).


The only proven benefit of vitamin D? Its role in helping the body absorb calcium and protecting our bone health. So, while evidence of its actual effects aren't yet conclusive, one thing is for certain: Your body needs it. Dr Sanjiv Chopra, hepatologist, best-selling author and Professor of Medicine at Harvard University gives us the facts.


1. Vitamin D is technically not a vitamin

Vitamins are organic compounds crucial for our bodies to develop and function normally. We can't produce enough of them, or at all, so most vitamins need to be obtained from food.


Vitamin D, on the other hand, can be produced by the body – our skin – when exposed to sunlight, specifically UVB rays. By that definition, it’s a hormone.

2. Why we need it

We know that Vitamin D absorbs calcium and phosphorous, and is crucial for building healthy bones and teeth. It doesn't stop there. In reality, nearly every cell in our body has a Vitamin D receptor so just about every type of tissue or organ in – including muscles, heart cells, brain cells and fatty tissue – requires it to function optimally.


It bolsters and regulates healthy immune system, and is just as important as other vitamins when it comes to fighting colds and flu.

In 2017, a global collaborative study of over 11,000 patients from 14 countries confirmed that vitamin D protects against colds and flu. People who took daily or weekly vitamin D supplements were less likely to report acute respiratory infections than those who did not.


3. What happens if you don't get enough vitamin D

Unsurprisingly, inadequacy can lead to a loss of bone density. Rickets (softening and weakening bones in children) is rare in developed countries but vitamin D deficiency may eventually lead to osteoporosis and fractures.

Researchers are still studying vitamin D for its possible connections to diseases like diabetes, cancer, cognitive disorders and autoimmune conditions. It's been tied to pregnancy complications, including gestational diabetes and pre-eclampsia (characterised by high blood pressure, fluid retention and protein in the urine ). In another study, a lack of the vitamin was shown to raise dementia risk.


What scientists and researchers do know: often when many serious diseases are diagnosed, Vitamin D deficiency is among the many biochemical abnormalities present.

4. Sufficient vitamin D levels may lower the risk of non-skin cancers

Vitamin D is a potent hormone for the regulation of cell growth, and some studies suggest it prevents cancer progression by slowing malignant cellular growth.

The risk of colon cancer, breast cancer and other malignancies appears to be more prevalent in populations living far from the equator. Minimal sun exposure and vitamin D levels may be part of the explanation.

In a Japanese study of over 30,000 people, researchers found high levels of Vitamin D were associated with a 20% lower relative risk of cancer in both men and women compared with low levels. Higher vitamin D levels also appeared to offer the clearest benefit for reducing liver cancer risk, especially for men.

5. Several factors impact your vitamin D levels

Age. Older people have a more difficult time producing ample amounts of vitamin D naturally as their skin thins and their metabolism slows.

Skin colour. The natural ability to produce vitamin D is also dependent on skin colour. Pigmentation can reduce the vitamin's production in the skin by over 90%. The darker the skin, the more difficult it is to absorb the UV rays necessary to produce it.

SPF. Sunscreen not only blocks the sun but also prevents the skin from getting the UV rays it needs to produce vitamin D. While we can't ditch the sun cream altogether, experts like Dr Chopra say we should expose our skin to the sun daily in short periods.


Where you live. People living in places farther away from the equator make less vitamin D in their skin as more UVB rays are absorbed by the ozone layer in these areas.

6. How much vitamin D do we really need?

There is no specific level that is universally defined as the right amount.


However much we need, a lot of us aren't getting enough whether it’s because we shun the the sun or slather on SPF. A National Health Survey found that 40% of Singaporeans are Vitamin D-deficient, despite the abundant sunshine we get.

“You need as much as you need,” says Dr Chopra. “And for each person that number is different depending on all the variables previously mentioned.”

In Singapore, the daily recommended amount for adults over 18 is just 100 IU a day, while

pregnant and breastfeeding women need 400 IU.


7. It's hard to spot Vitamin D deficiency

There are no specific symptoms, although common complains include overall fatigue, low mood, muscle aches and pains – which unfortunately, are also signs of countless other problems.


"It's good to have one's vitamin D3 levels checked," Dr Chopra says.


The only way to determine if you're deficient is with a blood test. Testing is particularly important for certain populations: individuals with multiple fractures, pregnant and breastfeeding women, dark-skinned individuals, veiled women, post-menopausal women and patients with inflammatory bowel disease and celiac disease.


8. Where to get vitamin D


You can get it the old-fashioned way and for free: the sun. Experts generally recommend that people spend 20 minutes a day outside in the sun without sunscreen. People with darker complexions should consider an additional ten minutes. You produce the most Vitamin D when you expose a larger area like your back, than the limbs or face.

The best time to nip outside? 10 a.m. to 3 p.m. or as Dr Chopra shares, "when your shadow is shorter than your height." Beyond that, he stresses that you should still use sunscreen to protect against skin cancer.

Food is the next option, though you may not be able to fulfil daily vitamin D needs just from diet alone as it's only found in a small amount of food. Reach for oily fish like mackerel (1006 IU/100g), wild salmon (988 IU/100g) and sardines (177 IU/100g). Egg yolks, mushrooms and fortified cereals also offer modest levels of vitamin D.

For that reason, supplements are a good idea to cover all your bases. In fact, Dr Chopra recommends taking them, “regardless whether one is deficient or sufficient.” He takes 4,000 IU of D3 daily.


There are two main forms of vitamin D. D3 is the type that your body produces when exposed to the sun's ray or synthesised from animal sources, whilst D2 is derived from plants like mushrooms. Most experts agree that D3 is likely more effective than D2 at replacing vitamin D in your system.


9. A final note: You can have too much of a good thing

While you can't overdose on vitamin D through exposure to sunlight, some doctors caution against taking more than 4,000 IU daily, pointing out that it is not usually needed and large doses increase the amount of calcium, which can have negative effects on your health and in some cases, can be toxic.



This article was supplemented with content from Dr Chopra's book, The Big Five: Five Simple Things You Can Do to Live a Longer, Healthier Life.


Dr Sanjiv Chopra, MD, is Professor of Medicine and former faculty dean for Continuing Medical Education at Harvard Medical School. He is also the Marshall Wolf Master Clinician Educator at Brigham and Women's Hospital, Boston; a bestselling author and sought after motivational speaker. Find out more about his work here.







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