️
Getting a tan might look like you’re soaking up the sun, but your body might not be making enough vitamin D. Here’s why — and how to fix it.
Table of Contents
1. Skin Color Affects Vitamin D Production:
Darker skin has more melanin, which protects against UV rays but also slows down vitamin D synthesis.
(Clemens et al., 1982: Skin pigmentation reduces vitamin D production efficiency.)
2. Sunscreen Blocks UVB Rays :
SPF protects your skin — but it also blocks the UVB rays your body needs to make vitamin D.
3. Time of Day Matters :
UVB rays are strongest between 10 a.m. and 3 p.m. That’s when your skin can make the most vitamin D.
4. Sunlight Through Glass Doesn’t Count :
UVB rays don’t pass through windows. So indoor sunbathing won’t help your vitamin D levels.
5. Tanning and Skin Aging Reduce Vitamin D Production :
Heavy tanning increases melanin, which blocks UVB. Aging skin also has less 7-dehydrocholesterol — the compound that turns sunlight into vitamin D.
(MacLaughlin & Holick, 1985: Aging skin produces 75% less vitamin D3 than young skin.)
6. Pollution and Clouds Block UVB :
Smog and thick clouds can block up to 60% of UVB rays, reducing your skin’s ability to make vitamin D.
7. The Angle of the Sun Is Crucial :
When the sun is low in the sky (early morning or late afternoon), UVB rays hit the Earth at a shallow angle and get filtered by the atmosphere. That means less vitamin D production. The angle at which sunlight hits your skin plays a major role in how much vitamin D your body can make. This angle is known as the solar zenith angle (SZA), and it changes depending on the time of day, season, and your location on Earth.
A 2021 study published in Photochemical & Photobiological Sciences found that vitamin D production was strongly correlated with the solar zenith angle — the lower the angle (i.e., the higher the sun), the more vitamin D was produced.
( Holick et al., 2004: At latitudes above 37°, UVB is too weak in winter to trigger vitamin D synthesis.)
If your shadow is longer than your body, the sun’s angle is too low for effective vitamin D production.
Best Practices for Safe and Effective Sun Exposure
- Expose arms, legs, or face for 15–30 minutes daily (depending on skin tone).
- Midday sun is best for vitamin D — but avoid burning.
- No sunscreen during short exposure, then apply if staying out longer.
- Don’t rely on windows — go outside!
- Bonus: Don’t Forget Food and Supplements
- Fatty fish, eggs, fortified dairy, and vitamin D supplements can help maintain healthy levels — especially in winter or if sun exposure is limited.
️
You must be logged in to post a comment.