Show HN: I built a daily sunlight tracker

>how most people aren’t getting enough

What are you basing this on? What counts as 'enough'? And how are you tracking light exposure?

There are countless studies that billions of people are Vitamin D deficient. Our bodies are designed to get most of that from the sun. Lots of people never even leave their house on a given day.

https://pmc.ncbi.nlm.nih.gov/articles/PMC3068797/

I should've been more specific. The study you link states that 'To prevent vitamin D deficiency, one should spend 15 to 20 minutes daily in the sunshine with 40% of the skin surface exposed.'. The screenshot on lume health shows a goal of 120 minutes.

Moreover, sun exposure is not by definition 'healthy'. Spending two hours in the sun at noon in the middle of summer does more harm than good.

> Nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group, indicating that avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking.

https://pubmed.ncbi.nlm.nih.gov/26992108/

"In the Fall of 2023, Apple introduced a new metric called “Time in Daylight” as part of watchOS 10 with Apple Watch Series SE (second generation) and Apple Watch Series 6 or later. This metric uses the ambient light sensor in Apple Watch and an associated algorithm to estimate how much time is spent in daylight and maximum intensity (lux) in 5-minute increments."

https://appleheartandmovementstudy.bwh.harvard.edu/summer-da...

Couldn't find any direct source from Apple tho

The study seems to be incredibly flawed.

> Women with active sun exposure habits were mainly at a lower risk of cardiovascular disease (CVD) and noncancer/non-CVD death

Not surprised there because people who spend more time outdoors will typically be participating in physical activity at the same time, while people who avoid sun exposure will typically be seated while participating in sedentary activities.

If we want to see if sun exposure is the sole reason for longevity, we will have to force the subjects to sit on a couch outside.

Claiming that not getting sunlight is the same as smoking is pure garbage.

Yes, you get your sun in the morning and/or in the evening. This is standard.

Where is the data here? That article simply declares that there is a global epidemic of vitamin D deficiency and I followed the citation it gives to back that up, which is this: https://www.sciencedirect.com/science/article/pii/S000291652.... Except this citation is also not a study. It's an opinion piece that just declares people are vitamin D deficient without doing any measurements of how much vitamin D anyway has circulating in their blood. It appears to be a narrative review, not a study.

I'm not saying the claim is for sure wrong, but at some point, to make this claim, someone has to have actually measured vitamin D levels in some broadly representative sample of humans and you could post that instead of whatever came up first in Google Scholar when search for "vitamin D deficiency."

> The study you link states that 'To prevent vitamin D deficiency, one should spend 15 to 20 minutes daily in the sunshine with 40% of the skin surface exposed.'. The screenshot on lume health shows a goal of 120 minutes.

Linearly it follows that if one wears clothes that cover more than 40% of lit skin, then the duration would be adjusted to match the total skin-area/time.

If one start with 1.85 m^2 body surface area, 40% of that is .72 m^2. If clothing covers 50% of a human and the human's shape and hair occludes half of that remaining, you have .46 m^2 available for sunlight. .72 m^2 * 20 is 14.4 m^2/min. divided by .46 m^2 it seems that 31.3 min would be the daily amount.

This seems much less than lume health's goal of 120 min. Otoh, given there is less opportunity for get to 14.4 m^2/min daily (I'm looking outside at a nice rainstorm), maybe the 120 min has some catchup factor?

> Claiming that not getting sunlight is the same as smoking is pure garbage.

So you're throwing out a whole study because it didn't cover a specific confounding variable you thought of, than stating a claim with no evidence backing it up?

That's pure garbage.

They specifically call this out in the abstract.

> We obtained detailed information at baseline on their sun exposure habits and potential confounders.

https://pubmed.ncbi.nlm.nih.gov/24697969/

Morning and evening sun are excellent due to the high levels of Near-IR and IR. However, it is devoid of UVB needed for vitamin D synthesis. You need morning, evening, and midday sun.

I think this mostly has been debunked in the last 15 years, except in the unscientific health influencer space

https://pubmed.ncbi.nlm.nih.gov/39017376/

This paper has a chart (figure 2) of the disease incidence prevention by serum vitamin D levels above the baseline of 25 ng/ml.

https://www.researchgate.net/publication/276034276_Vitamin_D...

Really the conclusion of that paper, that people are not vitamin D deficient, ought to be that people are sunlight deficient. This is why studies that involve supplementation of vitamin D frequently show no effect. Vitamin D is only one of many many ways in which light affects biology.

The paragraph near the end about babies needing fortified milk because breast milk is insufficient in vitamin D is laughable. It seems pretty obvious that babies are one of the most, if not the most, sunlight deficient demographics.