Unfortunately too many other changes happened at the same time. I am enormously healthier now (in numerous measurable as well as subjective ways) but it may be that the D levels played no role.
Not the same person here, but a data point nonetheless. Before supplementing D3 I had a cold basically every year, sometimes twice a year. Since I brushed up my levels I average 1 cold in 6 years.
Oddly, since the Covid time, I haven't caught a cold or flu once. I'm not sure it's the vaccines, the flu shots, or the less physical contacts on things overall. I still go to crowded places from time to time, like plane or train rides. May be the population in general have less cold or flu virus overall to go around.
for me, i was so deficient that i would notice it the next morning. also probably not a placebo as the D supplement i am taking is not something my mind goes to 7 am pre coffee lol