A lot of interesting research and opinions has been published during the last ten years. Here are a few links:

"Vitamin D deficiency in undifferentiated connective tissue disease". https://arthritis-research.biomedcentral.com/articles/10.118...

"The Big Vitamin D Mistake". https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5541280/

"For health professionals: Position statement on supplementation, blood levels and sun exposure". https://www.vitamindcouncil.org/for-health-professionals-pos...

"The effect of vitamin D supplement on the score and quality of sleep in 20-50 year-old people with sleep disorders compared with control group". https://www.ncbi.nlm.nih.gov/pubmed/28475473

"A Statistical Error in the Estimation of the Recommended Dietary Allowance for Vitamin D". https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4210929/

"Dosage of Vitamin D Needed To Achieve 35 to 40 ng/ml (90-100 nmol/L)". https://www.medscape.com/viewarticle/589256_8 (open in an incognito window to avoid the login screen)

"Vitamin D Status and Acute Respiratory Infection: Cross Sectional Results from the United States National Health and Nutrition Examination Survey, 2001–2006". http://www.mdpi.com/2072-6643/7/3/1933/htm

"Additional 4 ng of vitamin D reduced chance of infection by 7 percent". https://www.vitamindwiki.com/Additional+4+ng+of+vitamin+D+re...

"Vitamin D supplementation to patients with frequent respiratory tract infections: a post hoc analysis of a randomized and placebo-controlled trial". https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4553208/

I have more links to relevant material, but I have to stop somewhere ;-) As you can see, the body of evidence is growing.