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Vitamin D in Singapore: why so many of us are low, and what your blood test really means
Singapore gets sun all year, yet low Vitamin D results are common. The reasons have more to do with how we live than with sunscreen, and a single number on a lab report needs more interpretation than most people realise.
You can replenish Vitamin D with a tablet safely and cheaply. You cannot undo photodamage.Dr Stephen Chu, quoted in CNA Lifestyle, October 2026
Low Vitamin D in a sunny country sounds like a contradiction. It isn't. Most of us simply aren't in direct sun at the times, or for long enough, for our skin to make it. And when a result does come back low, the right response is usually to interpret it, not to panic.
Why low Vitamin D is common in Singapore
Your skin makes Vitamin D when UVB rays from the sun reach bare skin. Sunscreen gets most of the blame for low levels. It plays a part, but I don't think it is the main culprit here. The bigger issue is urban planning, and how we live in it.
You can go from your flat to the car park to the office to the mall and home again without ever being properly in the sun. Sheltered walkways, underground links and air-conditioning everywhere all reduce exposure, and office hours happen to cover exactly the part of the day when UVB is most useful.
Indoors by day
Office and shift workers get little direct sun. Ordinary window glass blocks most UVB, so a sunny desk does not count.
Skin tone
Darker skin has more melanin, which absorbs UVB. It takes more sun to make the same amount of Vitamin D.
Covering up
Long sleeves, umbrellas and avoiding a tan all reduce exposure, whether for modesty, comfort or a preference for fair skin.
Age and body weight matter too. Older skin makes Vitamin D less efficiently, and because Vitamin D is fat-soluble, people with more body fat tend to have lower blood levels.
What the blood test actually measures
Vitamin D made in the skin, or taken in from food and supplements, is converted by the liver into 25-hydroxyvitamin D, or 25(OH)D. This is the circulating, stored form, and it is what a standard Vitamin D blood test measures. The kidneys then convert it into the active hormone as the body needs it.
Labs report the result in one of two units, which causes a lot of confusion.
20 ng/mL is about 50 nmol/L, and 30 ng/mL is about 75 nmol/L. Check which unit your report uses before comparing it with anything you read online.
What counts as low? The experts don't fully agree
There is no single perfect Vitamin D level that applies to everyone, and the major expert bodies draw their lines in different places.
| 25(OH)D level | How it is usually interpreted |
|---|---|
| Below 12 ng/mL (30 nmol/L) | Deficient. Over time this can lead to soft, weak bones (osteomalacia) in adults. |
| 12 to 20 ng/mL (30 to 50 nmol/L) | Generally considered inadequate for bone health in healthy people. |
| 20 ng/mL (50 nmol/L) and above | Adequate for bone health in nearly everyone, according to the US Institute of Medicine. This is the most widely used cut-off, and the one Singapore studies generally apply. |
| 30 ng/mL (75 nmol/L) and above | The level the Endocrine Society's 2011 guideline suggested for at-risk groups, such as older adults at risk of falls or people with osteoporosis. |
| Above 50 ng/mL (125 nmol/L) | No added benefit shown. Linked to potential harm, particularly at higher levels. |
The 20 ng/mL figure is useful, but it was only ever meant as a population figure for bone health, not a personal optimum. Whether a particular number needs action depends on you: your bones, your risk factors and your symptoms.
One number on one day isn't a diagnosis
Vitamin D testing is less consistent than most people assume. One study comparing laboratories found results differing by around 12 nmol/L (about 5 ng/mL), and that included labs using mass spectrometry, which is meant to be the gold standard. A result of 18 ng/mL at one lab and 22 ng/mL at another may simply be the same blood measured twice.
Levels also move with recent sun, travel and supplements. So a borderline result needs interpreting against the whole picture of the person, not acting on straight away.
Comparing results from different labs or methods can make a level look as if it has gone up or down when it hasn't.
Getting sun, sensibly
I don't give patients a precise prescription of sun. The practical advice is simply to be a little less avoidant of it.
- Timing: go out mid-morning or late afternoon, when the sun is less harsh than at midday.
- Short and regular: brief exposure on most days does more than an occasional long session.
- Some skin uncovered: arms and legs, not just the face and hands.
- Direct sun: shade cuts UVB a lot, and glass blocks most of it.
- Never to the point of redness: reddening means you have gone well past what your skin needed.
This is not a reason to give up sunscreen. Use it properly and top it up if you sweat, rather than hoping incidental exposure will cover you.
If you are fair-skinned, have a personal or family history of skin cancer, or are treating pigmentation such as melasma, take a supplement instead. You can replenish Vitamin D with a tablet safely and cheaply. You cannot undo photodamage.
Tablets, food and how much
Supplements
Vitamin D3 (cholecalciferol) is the form most commonly used. For maintenance, the usual recommended intake is about 600 IU a day for most adults and 800 IU a day over the age of 70. A confirmed deficiency may need higher doses for a period, and that should be guided by a doctor who can recheck your level. Because Vitamin D is fat-soluble, it is usually best taken with a meal.
Unless a doctor is treating a deficiency, adults should not take more than 4,000 IU a day long term. Too much Vitamin D can raise blood calcium (hypercalcaemia), which can cause nausea, thirst, confusion and kidney stones, and in severe cases kidney damage and abnormal heart rhythms. Check combination products too, as doses add up.
Food
Few foods contain much Vitamin D. The best sources are oily fish such as salmon, sardines and mackerel, egg yolks, and foods fortified with Vitamin D, including some milks, plant milks, yoghurts and cereals. Some mushrooms are treated with UV light to raise their Vitamin D content; look for it on the label. For most people, food alone will not correct a low level.
Who should get tested?
Not everyone needs a routine Vitamin D test. It is most useful when the result could change what you do, for example if you:
- spend most daylight hours indoors, or work nights
- have darker skin and little direct sun
- are older, or have osteoporosis, low bone density or a fracture from a minor fall
- have a condition that affects absorption, such as coeliac disease, inflammatory bowel disease or previous weight-loss surgery
- take long-term medicines that affect Vitamin D, such as some anti-seizure drugs or steroids
- are pregnant or planning a pregnancy (discuss this with your doctor)
If you start supplements for a confirmed deficiency, a repeat test after around three months, at the same lab, shows whether the dose is working.
Vitamin D at Aquila Medical Center
Vitamin D can be included in our health screening, with results reviewed by a doctor alongside your history and other results. For a wider view of which tests are worth doing, see Which Health Screening Tests Actually Matter?
I also spoke to CNA Lifestyle about this topic: Why so many people in sunny Singapore have Vitamin D deficiency.
Questions patients ask
Does sunscreen cause Vitamin D deficiency?
It contributes, but in everyday use it is not usually the main reason. Time spent indoors and under cover matters more. Keep using sunscreen and, if your level is low, correct it with a supplement.
Can I make Vitamin D sitting by a sunny window?
Not much. Ordinary window glass blocks most of the UVB your skin needs.
How long should I spend in the sun?
There is no single safe number for everyone. It depends on your skin type, the time of day and how much skin is uncovered. Short, regular exposure that never reddens your skin is the sensible approach, and people with fair skin or a history of skin cancer are better off with a supplement.
My result is 25 ng/mL. Is that low?
It is above the 20 ng/mL cut-off most commonly used for bone health, but below the 30 ng/mL some guidelines suggest for at-risk groups. Whether it needs action depends on your bones, risk factors and symptoms, so it is worth discussing with a doctor rather than self-treating with high doses.
Can I take too much Vitamin D?
Yes. Long-term high doses can raise blood calcium to harmful levels. Unless a doctor is treating a deficiency, adults should stay at or below 4,000 IU a day.
Selected references
- Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academies Press; 2011.
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011;96(7):1911–1930.
- National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. ods.od.nih.gov
- CNA Lifestyle. Why so many people in sunny Singapore have Vitamin D deficiency – and what you should know. 2 October 2026.
This article is educational and does not replace individual medical assessment. Vitamin D testing and supplement doses should be guided by a doctor who knows your history. Written by Dr Stephen Chu, Founder and Medical Director, Aquila Medical Center, Singapore. Last reviewed: October 2026.
Have a Vitamin D result you are unsure about?
A doctor can review it alongside your history and other results, and advise whether anything needs to change.