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Comment by andreilys | Hacker News Reader

How do you balance wearing sunscreen with getting the necessary vitamin d exposure from the sun?

I put sunscreen on my face and neck let my arms and legs soak up vitamin D.

Everyone is vitamin deficient in one way or another. We all should supplement anyway, so just supplement vitamin D.

Supplementing vitamin D is unlikely to hurt in most cases (if you're taking a useful form like D3 and if you're not acutely deficient in vitamin A and K2), but it both isn't that effective on its own—oral supplementation tends to take a long time to fix deficiency and may work particularly poorly for people with absorption issues—and doesn't provide the full benefits of sun exposure (nitric oxide being a big one, but there are other immune, blood pressure, and inflammation benefits, as well as stuff related to how vitamin D is produced through sun exposure to the skin).

For me, better mental, cardiovascular, immune, and bone health is more important than apparent skin aging and a marginally increased risk of skin cancer, but everybody has to make their own trade-off decisions. A moderate amount of sun exposure is beneficial to most people. Avoid burning—especially severe burns with kids, which seem to be a big factor in eventual skin cancer risk—by controlling length of exposure and by wearing clothes to cover your skin if you can't control length of exposure.

Our skin needs a moderate exposure to the sun, like 3-4 times a week for 15 minutes in summertime.

If it were that simple…

Parameters that affect exposure time to produce a certain amount of vitamin D:

* Date, time

* Location

* Skin type

* Body exposure

* Clouds

* Ozone

* Elevation

* Surface

Here is a calculator from the Norwegian Institute for Air Research:

https://fastrt.nilu.no/VitD_quartMEDandMED_v2.html

https://fastrt.nilu.no/README_VitD_quartMEDandMED_v2.html

In addition, vitamin D requirements and synthesis might vary between people and health status.

Thank you for sharing the calculator. I see there are many external parameters to consider, and variety between people and health status adds to the compexity.

I think it renders the approach to calculate sun expose time unreliable and, probably, useless for most people. Are there other ways? Can I reliably measure my current and required levels of vitamin D, ideally without going to the doctor every week? Or could I just rely on common sense - make sure I spend time outside, but avoid exposing my skin for longer than 30 mins on sunny summer days?

I don’t know of any way that is more reliable or less risky. There are more accessible ways (e.g. maximize time outside without burning), but I wouldn’t think of them as reliable, safe or time-efficient.

Determining vitamin D levels will vary by country. You’d have to research how it works.

I’m not aware that healthy people can get too much vitamin D from the sun. In combination with the many beneficial effects of natural light (see melatonin, circadian rhythm, mood, etc.), maximizing time outside without burning seems like the best strategy to me. I just find it easier to avoid getting sunburn with the above calculator. Day-by-day variations are small enough that you might be able to make educated guesses most of the time and not check every time you go outside.

If this collides with one’s life (e.g. work-hours), supplements could be considered, but those come without the other effects of natural light.

To check the current UV index and ozone column:

https://www.temis.nl/uvradiation/nrt/uvindex.php

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