Do sunglasses block vitamin D? No. Your skin makes it, not your eyes

No, sunglasses do not block vitamin D. Vitamin D is made in the skin, when ultraviolet B light reaches it. The eyes are not involved at any step. Sunglasses block ultraviolet from reaching the eye, which is the whole point of them, and they have no effect on how much sunlight reaches your skin or how much vitamin D it makes. The claim that sunglasses cause vitamin D deficiency circulates widely and has no mechanism behind it. Here is where it likely came from, and what actually decides your vitamin D.

How vitamin D is made

Sunlight contains ultraviolet B, in the range of roughly 280 to 315 nanometres. When UVB reaches skin, it converts a cholesterol derivative in the skin cells into a precursor that the liver and kidneys then turn into active vitamin D. That is the entire pathway: skin, liver, kidneys.

The amount made depends on how much UVB reaches skin. That in turn depends on:

• How much skin is exposed. Arms and face in summer make plenty; a covered body makes little.
• Time of day. UVB is strongest in the middle of the day and weak in early morning and late afternoon.
• Season and latitude. In winter at higher latitudes, the sun is too low for much UVB to reach the ground at all.
• Skin tone. Darker skin needs longer exposure to make the same amount.
• Sunscreen. Blocks UVB by design, and reduces synthesis in proportion.
• Glass. Windows block most UVB; sun through a window makes little vitamin D.

Nothing in that list involves the eye.

Why the myth exists

The eye does respond to light, and that response does reach the rest of the body. Light entering the eye, particularly blue-rich daylight, tells the brain what time it is and sets the body clock, which affects sleep, alertness and hormones. That is real, it is well established, and it is why morning daylight matters.

It is also entirely separate from vitamin D. The body clock is a signalling pathway from the retina to the brain. Vitamin D is a chemical reaction in the skin. The two share a cause, sunlight, and nothing else. Someone who knew that light through the eye affects the body, and did not know how vitamin D is made, could put the two together and produce the myth. It has no support in the physiology.

A version of the claim sometimes adds that UV entering the eye signals the skin to make vitamin D, or that the pituitary gland is involved. There is no such signal. UV reaching the retina does one thing, which is damage it; that is why sunglasses block it.

What sunglasses do

Sunglasses block ultraviolet at the eye. That protects the cornea, the lens and the retina from cumulative UV damage, which eye-care bodies link to cataract and other conditions over a lifetime. That is the whole of their job, and it is unrelated to the skin.

Our lenses carry a UV-protective coating and every product page says so, with the limits of that claim stated. The UV400 vs polarized post explains what the labels mean.

If vitamin D is the concern

Then the levers are the ones in the list above: some skin exposed, around the middle of the day, for a period that depends on your skin tone and latitude, without sunscreen for that short window. In winter at higher latitudes, diet and supplements do what the sun cannot. Your sunglasses can stay on the whole time; they change none of it.

Wearing sunglasses and getting enough vitamin D are not in tension, and anyone who tells you to take your sunglasses off for your vitamin D is asking you to expose your eyes for no benefit.

Frequently asked questions