[DoodleBuggy]

Take the extremes; is cancer incidence markedly lower in perpetually sunny cities like Phoenix or Los Angeles compared to perpetually cloudy cities like Seattle or Portland? Surely the data would show if there were a notable difference for people exposed to 11 months of sun versus 10 months of clouds.

[rm999]

That's almost exactly how they found the connection, from the article:

> Early epidemiologic research showed that incidence and death rates for certain cancers were lower among individuals living in southern latitudes, where levels of sunlight exposure are relatively high, than among those living at northern latitudes

An obvious problem is confounding variables, this isn't a controlled correlation in any way. The article goes on to say:

> However, additional research based on stronger study designs is required to determine whether higher vitamin D levels are related to lower cancer incidence or death rates.

[rnprince]

This reminds me of autoimmune disease like MS. They are more common in higher latitudes (where there happens to be less sunlight), and there is a connection to low Vitamin D that isn't understood.

While attempting to understand the link better, UW-Madison researchers recently produced data implying that the ingredients of some sunscreen products may provide benefit in preventing MS. https://www.acsh.org/news/2017/07/28/sunscreen-ms-and-hard-b...

[tonyedgecombe]

There was a piece in the New Scientist a couple of years ago that said type 1 diabetes seems to be correlated with higher latitudes. They suggested it was related to Vitamin D.

[rnprince]

Yes, like MS, type 1 diabetes is considered to be an autoimmune disease. It's surprising to me as someone who hasn't studied medicine how related to each other autoimmune issues seem to be. Rheumatoid arthritis and latitude is another one that follows this same pattern. This article from 2010 about rheumatoid arthritis also mentions the link to low vitamin D levels, and that the link isn't understood.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2920915/

[_0w8t]

Are there any statistics that low levels of D at northern latitudes decreases life span? Without such decrease even if it will be confirmed that low D causes cancer, it will also imply that higher levels of D causes other problems that just as deadly as cancer.

[cellularmitosis]

One example (mentioned elsewhere in this thread) is that incidence of autoimmune disorders goes up as you get farther away from the equator

Edit: I suppose that’s decreased health span more than decreased life span

[_0w8t]

As D suppresses immune system among many other things one should not be surprised to have such correlation with incidents of autoimmune disorders. On the other hand life span in Canada is few years longer than in US while I got impression that levels of D deficiency is comparable in US and Canada. So I guess it is very open question if low D is really bad.

[AstralStorm]

Additional research such as EPIC series of research? One of which studied the impact of vit. D levels in blood on all cause mortality corrected for many factors?

(Note: EPIC studies Europeans.)

[jaequery]

idk, being too sunny also leads to staying indoors more. especially in LA. i rarely get sun around here. just the other day, my doctor told me i have extremely low levels of vitamin D. and i started taking 10k mg doses of vitamin D, this also seem to help me sleep better at night.

[StavrosK]

Why not just go out and walk more?

[ovao]

Which is a great idea for more than just the sun exposure, but unfortunately at Los Angeles's latitude, there isn't sufficient UVB to trigger vitamin D production in the skin from around the beginning of October through the beginning of March. During these months vitamin D supplementation is pretty much a necessity for anyone who's ordinarily vitamin D deficient.

[bdamm]

The root cause here is probably high stress, to which walking more is probably going to be helpful, but for people under chronic stress (as I am from time to time) it can be hard to see how to make the time for that.

[ianai]

I used to walk when I lived in a different neighborhood of a southern city. We get lots of sun, but way more heat & pollution. My neighborhood's simply not great for walking.

[samcal]

You can do both! But if you supplement vitamin D you wouldn't need to worry about making it out for your walk every day. IANA nutritionist, but I also believe GP's prescribed dose would be unfeasible to get reliably from the sun, especially at northern latitudes.

[StavrosK]

Hmm, I see. I live in Greece, so I don't really have an intuition for how much sun one needs (we get eight months of sun or so). What you say makes sense, thank you.

[ovao]

The Norwegian Institute for Air Research has a fairly simple online calculator: https://fastrt.nilu.no/VitD-ez_quartMED.html

I can't personally vouch for its accuracy though.

[seanwilson]

Doesn't sun exposure cause skin ageing and increase your risk of skin cancer?

[ianai]

It does - so much so that fair skinned people are suggested to avoid sun exposure and get vitamin d from supplements.

[coldtea]

Not unless you overdo it.

[bproven]

Agreed - I think this is another myth that has gone mainstream. The biggest issue from my reading is damage to the skin. If you are constantly getting burned you are increasing your risk. If you slowly increase your exposure and avoid burning you get the benefits of sun plus (almost) none of the drawbacks. I say almost b/c you cannot discount genetic predisposition. Also, time of day is critical too - with mid-day being the best time.

I'm not sure if there are studies that take this variable into consideration. The tin foil hatter in me tends to think the results are probably different than the current common belief. BUT we can't have sunscreen sales dropping to zero ;) BTW I'm also weary of the effects of sunscreen itself - does slathering chemicals on your skin to protect against sun contributing to cancer?

Th truth is there is probably a happy medium somewhere between the "sun is evil! It causes cancer!" and "don't worry worshipping the sun is OK". However we tend to knee jerk react in one direction or the other...

[dvtv75]

It's not always that simple - in Dunedin, NZ, burn time can be under ten minutes. It's quite similar in Australia, too.

[FTA]

Another consideration is the pollution you're breathing when walking or deeply breathing while running. Particulate matter, ozone, and carbon monoxide could very well cancel out the benefits of receiving that Vitamin D production you get in some months.

[trhway]

>Take the extremes; is cancer incidence markedly lower in perpetually sunny cities like Phoenix or Los Angeles compared to perpetually cloudy cities like Seattle or Portland?

you need to compare not the whole populations of geographies - you nee to look at people who isn't evolutionary adapted (in this particular case - skin color to manage the sunlight and vitamin D level in particular) to the geographies they are currently living at.

For example, children autism is much higher in the Somali immigrant population in Minnesota and Sweden (vs. Somalis in Somali) as this immigrant population has, for obvious reasons, extremely low, frequently almost non-detectable, vitamin D levels.

If cancer rate has negative correlation with vitamin D levels, we'll, unfortunately, see it for sure in like a decade or 2 in those immigrant populations.