Sunscreen blocks 95% vitamin D? Doctor shares 11 eye-opening facts you should know about vitamin D

Vitamin D is often called the “sunshine vitamin,” but as Dr Priyam Bordoloi highlights on X, it’s far more than a simple nutrient. For billions of people, understanding how it works in the body could change the way we approach everything from bone health to mood, immunity, and heart function. From how sunlight, skin tone, and magnesium influence absorption to its role in regulating serotonin, insulin, and blood pressure, these facts reveal why vitamin D is critical—and surprisingly complex.

Vitamin D is a hormone?

Dr Priyam Bordoloi explains that vitamin D is technically a hormone, not just a vitamin. It requires ultraviolet light from sunlight to activate, meaning exposure matters. Yet modern habits can block its benefits: sunscreen with SPF 30 can reduce the skin’s vitamin D production by roughly 95%, and darker skin tones need three to five times longer sun exposure to achieve the same levels as lighter skin. Without adequate vitamin D, the body can absorb only about 10–15% of dietary calcium, highlighting its essential role in bone and overall mineral health.

Magnesium is a factor for Vitamin D

Magnesium is another crucial factor. The body cannot properly activate or transport vitamin D without it, making it a mandatory cofactor for optimal function. Deficiency in vitamin D has broader effects than bone health alone; it has been linked to seasonal mood changes, sometimes referred to as “Winter Blues,” because of its influence on serotonin and dopamine regulation in the brain. It also enhances insulin sensitivity, supporting pancreatic beta-cell function, and acts as a natural “brake” on the Renin-Angiotensin system to help regulate blood pressure.

Impact of Vitamin D

Vitamin D’s impact extends to cardiovascular health as well, preventing “ectopic calcification,” a condition where calcium deposits in arteries rather than bones. It also boosts the immune system by enhancing T-cell activity, helping the body fight infections more effectively. For those taking supplements, absorption can be significantly improved—by up to 32%—when taken with a meal containing fat.

Dr Priyam Bordoloi’s insights underscore how vitamin D is central to multiple systems in the body. Sun exposure, dietary cofactors like magnesium, and careful supplementation are all key to harnessing its full benefits. For a nutrient that touches everything from mood and immunity to calcium metabolism and heart health, understanding vitamin D is essential for long-term wellness.

Vitamin D-rich foods

As per Healthline, vitamin D can be found in both animal and fortified plant sources, making it possible to meet your daily needs through diet. Fatty fish like salmon and mackerel are among the richest sources. Eggs provide modest amounts, which can be increased through UV-exposed or high-vitamin D hens. Mushrooms exposed to sunlight produce vitamin D2. Fortified foods like cow’s milk, soy milk, and orange juice also contain vitamin D, and supports bone and immune health.