[docflabby]

People who avoid the sun more likely to take vitamin D supplements?

[jmckib]

I don’t have access to the full paper, but I would expect that they at least tried to control for sun exposure.

In general, if you can think of an obvious confounding factor in about five seconds, then it’s a safe assumption that professional researchers thought of it too.

[kixiQu]

Or, at least, a safer assumption: it's worth checking to see what they said about it before publicly speculating.

And indeed, it seems they did survey for sun exposure and include it in their analysis, and they caveat a lot of their references to other work in their introduction noting where other studies didn't.

https://www.naturalhealthresearch.org/wp-content/uploads/202...

[Calavar]

> In general, if you can think of an obvious confounding factor in about five seconds, then it’s a safe assumption that professional researchers thought of it too.

I work in academic medicine. I read a lot of papers. This is not at all a given in my experience, except maybe in the tippy top journals (Nature, NEJM). When in doubt, read the paper, see if they mention the confounder you thought of.

[Gimpei]

They probably have, but that doesn’t mean they have the necessary data to actually address the confounds. Often there is a trade off between what is most provable and what is most novel. Publishing incentives being what they are, novel invariably wins.

[mlinhares]

The study is based on a couple hundred people in a city in Finland, they could at least have tried to collect data on people closer to the tropics to hedge a bit. I doubt this has any validity ignoring such a basic confounding factor like living in a place that does have a lot of sun exposure.

[surfpel]

> safe assumption that professional researchers thought of it too

Research should be able to stand up to scrutiny. The scientific process depends on it.

Given the ongoing reproducibility crisis and plethora of garbage research coming out of academia, I’m not assuming anything about any research I see.

[andreareina]

Accounting for confounders is hard. Otherwise randomised controlled studies wouldn't be needed, and we'd not have taken this long to walk back the consensus that red meat causes cancer.

[beowulfey]

Here is the description how they measured the impact of sun exposure to the results:

> The exposure of skin to UV radiation was clarified with different questions. The self-estimated lifetime exposure was studied with the following question ‘How often have you exposed yourself to sunlight during your lifetime?’ The answer options were (1) ‘seldom’, (2) ‘occasionally’, (3) ‘often’, or (4) ‘very often’. The sunburn history was studied with the following question: how often has your skin been burned due to sunlight during your lifetime? The answer options were (1) ‘seldom’, (2) ‘occasionally’, or (3) ‘often’. The answer options for the question of ‘Main environment in working history’ were (1) ‘outdoor’, (2) ‘indoor’, or (2) ‘variably both’.

They saw approximately the same distribution of sun exposure across the different test groups, it looks like.

[itake]

I wish they asked exact rates and timelines. Like living in Florida, getting a bad burn only once per year might be considered seldom. But if you lived in Alaska, I’m sure that would be qualify as often.

[krona]

I think just as likely is the general problem of people who take supplements being generally more conscientious and less likely to engage in risky behaviours (e.g. wearing sunscreen in summer)

[DoesntMatter22]

Or they are supplementing because they don't get much sun to begin with

[reader5000]

People who avoid the sun are less likely to care about health overall and therefore less likely to take vitD supplements?

[mlinhares]

Or people that frequently supplement vitamin D live in places where there isn’t much sun hence the supplements.

[ericmcer]

Yeah… doctors recommend supplementing vitamin D if you don’t get much sun. This almost feels comedic.

[lowmagnet]

Doctors recommend supplementing vitamin D if you have a measured deficiency. Most people naturally settle to 20 ng/mL or higher, and just incidental exposure, or eating certain foods can help you either absorb or synthesize it.

There are also people, like me, who no matter what, we can't make as much vitamin D for whatever cluster of genetic factors causes that. Some of us are always tired unless we take 50,000 IU of D3 a week.

[cj]

Did the study not control for confounding factors?

[Gibbon1]

Tweedledee: People with less sun exposure both intentional or unintentional may supplement more.

Tweedledum: Low Vitamin D weakens your immune system. Having a weakened immune system increases your odds of skin cancer.

[nemo44x]

Yeah my immediate thought too. Give 2500 rabid tanners vitamin D and let’s look at skin cancer rates in 10 years vs the population of rabid tanners.

[rayrey]

I assume the rabies will get them first

[kwhitefoot]

So do people who live in high latitudes where there is very little sun in the winter and it is too cold anyway to reveal enough skin.

[psychphysic]

Conversely, those people who refuse to ever cover up "cause you need vitamin D".

[jasonsb]

This is the most plausible reason.

[experimenting]

The most plausible reason is that the scientific peer-reviewed result is correct, not the tiring "correlation does not imply causatian" commenter on HN who at most skimmed the paper.

2009: > Epidemiological data show an inverse relationship between vitamin D levels and breast cancer incidence. In addition, there is a well-documented association between vitamin D intake and the risk of breast cancer. Low vitamin D intake has also been indicated in colorectal carcinogenesis. A vitamin D deficiency has also been documented in patients with prostate cancer, ovarian cancer, as well as multiple myeloma. Larger randomized clinical trials should be undertaken in humans to establish the role of vitamin D supplementation in the prevention of these cancers.