A review of vitamin D meta-analyses reporting on all-cause mortality yields a meta-analytic result of RR=0.96 with little heterogeneity or signs of bias. Reproducing it as a Bayesian random-effects meta-analysis gives a posterior predictive probability P=84% that RR<1.0. The expected life expectancy gain is 0.33 years or $16,800, while total cost of vitamin D supplementation is estimated at $761, for a profit of $15,300. The probability of being profitable is estimated at P=83%. The optimal beginning age is 24yo.
See also: https://www.gwern.net/Longevity#vitamin-d