Sunlight and Vitamin D: Separating Fact from Fiction

Vitamin D is a fat-soluble secosteroid nutrient that aids in calcium absorption, promoting bone growth and health [1]. It acts like a hormone and plays a key role in regulating cellular activity and immune system function. Despite its well-established importance, a significant portion of the global population remains at risk of insufficient vitamin D levels [2,3].

The Institute of Medicine (IOM) classifies sufficient vitamin D levels as serum 25-hydroxyvitamin D (25(OH)D) readings above 50 nmol/L. Studies suggest that one reason for the widespread deficiency is limited knowledge about vitamin D [4–6].

Vitamin D can be obtained through food, although natural dietary sources are limited. Examples include deep-sea fish (such as salmon and mackerel), mushrooms, and fortified foods. As a result, the primary source of vitamin D is sunlight. Known as the "sunshine vitamin," direct exposure to ultraviolet B (UVB) rays allows the skin to produce vitamin D.

Although this concept seems straightforward, proper knowledge is essential to safely benefit from sun exposure. My qualitative research uncovered several myths and misconceptions about vitamin D. Seven focus group interviews were conducted among female indoor workers with vitamin D levels below 50 nmol/L (insufficient) before the COVID-19 pandemic [7]. The interviews revealed that inaccurate information was one of the main causes of insufficient vitamin D levels.

1. Myth: Vitamin D can be obtained from vegetables and fruits.

Fact: The primary source of vitamin D is sunlight (UVB rays). Natural dietary sources are limited, including eggs, beef liver, and deep-sea fish. Plant-based sources are limited to mushrooms. Vitamin D is also available in fortified foods such as cow's milk, yogurt, butter, and biscuits.

2. Myth: Vitamin D can be generated through sunlight passing through car or window glass.

Fact: UV rays that help generate vitamin D are UVB rays, which cannot pass through glass. Only UVA rays penetrate glass, but they do not produce vitamin D. Therefore, no vitamin D is generated when sunlight passes through glass windows.

3. Myth: Malaysians have sufficient vitamin D levels because we receive sunlight year-round.

Fact: Studies on vitamin D levels in Malaysia since 2011 have found that several groups are at risk of deficiency, including women [8], children and teenagers [9,10], urban populations [11], indoor workers [12], and those of Malay and Indian ethnicity [13].

4. Myth: Vitamin D is obtained only from morning sunlight.

Fact: Vitamin D can generally be generated between 9 AM and 5 PM, when UVB rays are present. However, UVB radiation levels depend on the sun's angle, location, and the amount of exposed skin. In Malaysia, UVB rays are strongest between 12 PM and 2 PM. Sun exposure without protection is recommended during low UV index hours (UV index of 3 or lower), typically before 10 AM or after 4 PM. If exposed during high UV index hours, use sunscreen or limit exposure to 30 minutes to avoid skin damage. Below is the daily UV Index chart by the Malaysian Meteorological Department, which shows UV levels across Malaysia.

By addressing these inaccuracies, we can collectively correct public knowledge and perceptions about vitamin D. Let’s share these facts and empower everyone with the right information to enhance their health and well-being.