The Irony Under the Sun: Why Is Vitamin D Deficiency So Common in a Tropical Country?
Here's one of life's biggest ironies: Despite living in the tropics and being blasted by the sun's rays all year round, about 40% of Singaporeans are deficient in Vitamin D, and 8% are very deficient, according to the 2010 National Health Survey by the Ministry of Health.
If you're wondering what the connection is, sunlight – more specifically UVB – triggers a chemical reaction in your skin to naturally produce Vitamin D. Think of your skin as a Vitamin D factory. When sunlight hits bare skin, UVB starts a chemical reaction that results in pre-Vitamin D. Your liver and kidneys then process it into 25-hydroxyvitamin D (25(OH)D), the form your body can use. Blood tests measure this as your Vitamin D "storage tank."
What's Stealing Your Vitamin D? Urban Living Is the Main Culprit
"Everyone blames sunblock," said Dr Stephen Chu, founder and medical director of Aquila Medical Center. "It plays a part but I don't think it's the main culprit in Singapore. The bigger issue is urban planning and how we live in it."
He explained that "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 walkways, air-conditioning everywhere, and office hours happen to cover exactly the part of the day when UVB is useful.
- Indoor workers at higher risk: A 2019 study involving 213 indoor workers found Vitamin D deficiency in nearly 33% of participants. Office workers, workshop workers, and night-shift workers were at greater risk.
- Sitting by a sunny window doesn't help: Ordinary glass blocks most of the UVB needed to make Vitamin D. Being in the shade also reduces UV exposure, said Dr Sueziani Binte Zainudin, a senior consultant endocrinologist from Ascensus Health.
- Skin tone matters: Having a darker complexion means more melanin absorbs UVB before it can trigger Vitamin D synthesis. A 2013 study on 197 women in Singapore found deficiency was more prevalent in Malay women (89%) and Indian women (82%) compared to Chinese women (56%).
- Gender differences: About 54% of females are Vitamin D deficient compared to roughly 30% of males. Women tend to cover up more or stay out of the sun due to cultural practices and social preferences.
- Weight matters too: Obesity has been suggested as a risk factor because the fat-soluble vitamin is readily stored in body tissue, preventing the body from using it. Obese subjects had 57% lower Vitamin D levels than leaner subjects.
- Elderly at high risk: In a local study of 134 subjects aged above 65 in a Singapore rehabilitation centre, 44% were found to be deficient, while nearly 86% had low levels.
Why Is Vitamin D Important? More Than Just Bone Health
Vitamin D is especially crucial for pregnant women. It supports calcium and phosphate metabolism needed for foetal skeletal development. A small 2024 study found that out of 93 participants in their first trimester, only 2.2% of mums-to-be had sufficient Vitamin D. Among Malay and Indian pregnant women, all were deficient.
For non-pregnant individuals, Vitamin D matters too. Its deficiency has been associated with a range of conditions:
- Osteoporosis: Vitamin D prevents it by helping the body absorb calcium to build bone and support muscle strength – highly beneficial for menopausal women and seniors with sarcopenia.
- Cancer risk: Linked to lower cancer incidence, most notably colorectal cancer, breast cancer, and prostate cancer.
- Diabetes and hypertension: Associated with a reduced risk of Type 2 diabetes, along with lowering blood pressure, which reduces the risk of heart attacks and strokes.
- Sleep and energy: Morning sunlight contains blue light wavelengths that increase cortisol and suppress the sleepy hormone melatonin. If you have difficulty dragging yourself out of bed, try drawing the curtains and letting the sun in.
How to Scientifically Supplement Vitamin D?
If you're concerned about Vitamin D deficiency, consider a blood test to confirm your levels. Here's how to improve:
- Expose your arms and legs to sunlight for 10-20 minutes daily during non-peak hours (avoiding 10 AM to 4 PM strong UV).
- Increase intake of Vitamin D-rich foods such as fatty fish, egg yolks, and fortified dairy products.
- Use Vitamin D supplements under medical guidance if necessary.
- Maintain a healthy weight to avoid obesity impairing Vitamin D utilization.
Want to better track your Vitamin D levels, blood pressure, blood sugar, and sleep quality? The Xiaoshu Health App can sync with Apple Health to track related metrics, helping you comprehensively manage your metabolic and bone health.