💊 Is vit D from supplements the same as vit D from the sun?

Vitamin D synthesis from sunlight is a complex biological process.

It begins when solar UVB rays with wavelengths of 290–315 nm that convert cholesterol (specifically 7-dehydrocholesterol) in the skin into a precursor of vitamin D.

Over approximately eight hours, this precursor undergoes several transformations (most still dependent on the sun) to become active vitamin D.

Once formed, vitamin D enters the bloodstream and binds completely to its carrier protein, which transports it to the liver for storage.

This form of vitamin D is heat-stable and remains in circulation 2 to 3 times longer than vitamin D obtained from food or supplements.

In contrast, dietary or supplemental vitamin D must be digested and absorbed through the gut.

It is then packaged into chylomicrons, enters the lymphatic system, and then the bloodstream.

Only about 60% binds to the carrier protein, and just 40% is taken up by cells; making it less efficient than skin-derived vitamin D.

🥊 Summary

Sunlight-derived vitamin D is a longer process, but offers superior stability and longevity of vitamin D in the body compared to dietary sources or supplements.

☀️ Can I just take vit D supplements and skip sun exposure?

Taking vitamin D supplements provides the final product of a complex biological process and helps meet dietary recommendations.

However, when vitamin D is synthesised in the skin through sun exposure, it produces additional compounds with unique health benefits.

Key by-products of sunlight-driven vitamin D synthesis include lumisterol and tachysterol, which are not generated through supplementation.

Lumisterol, for example, can be converted into active molecules with potential anti-tumour effects, such as reducing UV damage and inhibiting excessive skin cell growth.

Moreover, sunlight exposure triggers other physiological responses in the skin.

These include enhancing immune modulation, boosting β-endorphin and nitric oxide production; all of which contribute positively to metabolic health.

🥊 Summary

Sensible sun exposure that produce pre-vitamin D, vitamin D and its photoproducts may have some additional benefits, such as prevention against skin carcinogenesis, above and beyond taking a vitamin D supplement.

🧴 Sunscreen and vitamin D: striking the right balance

Sunscreens are designed to absorb solar UVB radiation, and a product with SPF 30 typically blocks around 95–98% of it.

While this protects the skin from damage, it also significantly reduces the skin’s ability to produce vitamin D by the same amount.

This happens because ingredients like para-aminobenzoic acid inhibit the conversion of cholesterol into previtamin D in the skin.

Interestingly, farmers in the Midwest USA who consistently used sunscreen were vitamin D deficient despite high sun exposure.

This highlights a key issue: sunscreen users can still suffer from low vitamin D levels, especially when combined with poor dietary intake.

Living indoors during the week and relying on weekend sun exposure while wearing sunscreen can lead to skin damage, vitamin D deficiency, and accelerated ageing.

A better approach is to build a ‘solar callus’: a gradual adaptation to sunlight through balanced and safe exposure to full-spectrum light (UVA, UVB, and infrared) starting in spring.

This naturally thickens the skin’s outer layer and evenly distributes melanin, acting as nature’s own SPF.

🥊 Summary

Sensible, progressive sun exposure supports healthy vitamin D levels and protects the skin more effectively than bursts of UV light even if wearing sunscreen.