[devaboone]

That is a reasonable hypothesis. Also, people who are very ill are less likely to get outside and get enough sun, so they will develop low Vitamin D. Vitamin D is likely a marker of poor health. (Once the Vitamin D gets low enough, we do see direct harmful effects from it (think rickets in children), and this may contribute to poor health at that point.)

[bakul]

Have there been any studies that test if the absorption of Vitamin D (from supplements) is influenced by disease compared to healthy people?

[tarsinge]

I’m healthy, fit and relatively active (3-4 hours exercise / week, 30-1h walk everyday), and I just tested relatively low in Vitamin D (before winter even started). What should I do?

[glofish]

As the paper states the only effect of Vitamin D supplementation is that it reduces Vitamin D deficiency.

[citruscomputing]

Talk to your doctor.

[mancerayder]

You must have some great doctors to ask questions like these to. In my experience there's nothing cutting edge about any answers I ever got from a doctor, and more often than not it's a predictable, nothing-to-see-here attitude. And I learned long ago to be cautious when I say something like, "I was reading about a study that suggested..." as you risk getting pinned with the loons at worst, and mostly ignored at best.

[tarsinge]

I’m not sure my doctor has access to better studies than what is in the TFA. My question is weirdly formulated, what I ask is is supplementation useless given what we know? Or is it safer to stay in the (arbitrary?) recommended range? What I get from the parent post is that given low vitamin D is a symptom of poor health, supplementation is useless if someone is in good health.

[pmiller2]

The thing with vitamin D supplementation is that, as TFA mentions, low to moderate doses (under 4000 IU per day) are generally very safe. And, being deficient in such a crucial nutrient certainly isn't a good thing. So, if you are deficient, supplementing in that range is probably something you could feel comfortable doing on your own. If it were me, I'd go out and buy a bottle of D3 and get my levels tested at my next checkup.