[Bonny]

Link between Vitamin D and IGF; seems they may work in synergy

https://www.medpagetoday.com/endocrinolo...logy/40932

https://examine.com/supplements/vitamin-d/

"....The recommended daily allowance for Vitamin D is currently set at 400-800IU/day, but this is too low for adults. The safe upper limit in the United States and Canada is 4,000IU/day. Research suggests that the true safe upper limit is 10,000IU/day. For moderate supplementation, a 1,000-2,000IU dose of vitamin D3 is sufficient to meet the needs of most of the population. This is the lowest effective dose range. Higher doses, based on body weight, are in the range of 20-80IU/kg daily.
Vitamin D3 supplementation (cholecalciferol) is recommended over D2 supplementation (ergocalciferol), since D3 is used more effectively in the body.
Vitamin D should be taken daily, with meals or a source of fat, like fish oil....."