alt Hacker NewsStudy was in an elderly cohort with cognitive impairment. This is a cohort more likely to have nutrition and diet problems and spend all of their time indoors. I haven’t found the full study but the results look marginal for a narrow group.
Then there’s this important note in the highlights:
> Higher daily Vitamin D intake may impact cognition in persons with sleep disturbance and MCI.
More is not better with Vitamin D. Correcting deficiencies is good but the mega dosing trend is not.
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I'd like to add that correcting deficiencies implies seeing a physician to get your dosage right. This is necessary both for Vitamin D and Melatonin.
If you're not a sedentary geriatric with MCI this study is probably not for you.
This guy will get you killed. It is reasonable to maintain a blood level of about 45 ng/mL. This often requires 5000 IU/day, perhaps less in seniors with weaker kidneys, or those with heavy sun exposure which is dangerous for other reasons. You don't need to see a doctor for this, but you do need to get the test done every year or two. Personally I prefer not involving a doctor for any of it.
Nobody disputes that excessive vitamin D is not good, but maintaining a blood level below 45 ng/ml also is not good. Covid studies had ascertained that a level of at least 50 ng/ml was optimal.
Don't go overboard, but you have quite a bit of margin for error. I am finding one claim that the upper maximum daily dose for Vitamin D is 4000 IU. A Costco daily multivitamin is 400 IU (most adults are recommended at 600 IU).
If you start supplementing with a traditional, OTC Vitamin D option, likely very low risk of complications.