I don’t think there’s anything definitive. 400IU/day from one study is nothing if you’re deficient. 2000IU from another study is better, but even then we don’t seem to know much about absorption from these studies. For example, did it actually raise serum levels by 10ng/ml after a year, and how did THAT correlate to positive or negative health outcomes? K2 also seems to play an important symbiotic relationship with D, and seems notably absent from these studies.

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adgjlsfhk1 a day ago | parent [-]

if supplements don't absorb and therefore don't affect health, there's no reason to take them.

	▲	grep_name a day ago \| parent [-]
		You missed the K2 part of his comment though. Both my mother and I have chronically tested incredibly low for vitmain D, both always taken supplements, both never had improvement. A couple years ago, my mom texted me saying she tried a D3+K2 supplement and for the first time in her life tested in range for vitamin D on her panel. I was skeptical but tried it, and have tested in normal range since.