The body synthesizes vitamin D when skin is exposed to sunlight. However, some individuals still experience vitamin D deficiency despite consistent sun exposure. Below are common reasons why this occurs.

**Underlying Medical Conditions**

According to the Times of India, sun exposure is merely the initial step in vitamin D production. After its formation in the skin, vitamin D needs to be metabolized by the liver and kidneys into its active form for the body to use. Several conditions can disrupt this process, including: chronic liver disease, kidney disease, Crohn's disease, celiac disease, and other conditions that cause fat malabsorption. Healthy adults typically require 600-800 IU (equivalent to 15 to 20 micrograms) of vitamin D daily.

**Sunscreen and Protective Clothing**

Sunscreen protects the skin from the harmful effects of ultraviolet (UV) rays, but it also reduces the amount of UV radiation necessary for vitamin d synthesis to reach the skin. When high SPF sunscreen is applied and covers large areas of the skin, this vital process can decrease.

Similarly, sun protection shirts, wide-brimmed hats, gloves, or other protective clothing that cover the skin also limit sun exposure. This can lead to lower vitamin D levels, even for individuals who regularly work outdoors.

**Darker Skin Pigmentation**

Melanin, the pigment responsible for skin color, helps protect the skin from sun damage. However, it also reduces vitamin d synthesis. Individuals with darker skin tones often require longer sun exposure to produce the same amount of vitamin D as those with lighter skin.

Eating fish helps supplement vitamin D. Photo: Bui Thuy

**Age-Related Decline in Production**

As people age, the skin's efficiency in producing vitamin D from sunlight decreases. Older adults may have similar sun exposure to younger individuals, but the amount of vitamin D generated remains lower. This is a common factor contributing to vitamin D deficiency among middle-aged and older adults, especially if they are less active outdoors.

**Vitamin D-Deficient Diet**

While sunlight is a significant source of vitamin D, food also contributes to maintaining its levels in the body. If a diet lacks fatty fish, eggs, and vitamin D-fortified foods, the dietary intake might be insufficient, particularly when the body's vitamin d synthesis is reduced. This risk can be higher for individuals following restrictive diets or unbalanced vegetarian diets.

**Recommendations**

Everyone should maintain a varied diet and appropriate sun exposure, while actively avoiding sunburn. Individuals at risk of vitamin D deficiency or with deficient test results should consult a doctor. Depending on the specific case, a doctor may prescribe appropriate supplementation.

Le Nguyen (Compiled)