My D3 levels have been tested 1-2 times per year for 2 decades. Despite not using sunscreen and D3 supplementation titrated by my MD, my levels were falling. Neither he nor I know why. He upped my D3 dose and my levels returned to where he wants them. Most people do not have optimum D3 levels. K2 is also important.
The attached is a bit technical but shows an important role for D3....
I paid my Doc a visit recently 5 days after breaking 9 bones in an accident, some of them with multiple breaks and one compound fracture. He adjusted my supplements/vitamins. I focused on lots of dark leafy greens, sardines, and more protein than usual. It is impossible for an N = 1 observation to differentiate positive effects. For instance, I would normally have a couple of beers Fri-Sun but stopped all alcohol, what is that effect? I know that 4 of my broken ribs healed in 5 weeks and the smashed clavicle was probably completely healed in 4 weeks. The Surgeon at 5 weeks said I have no limitations on the compound fractured humerus and the smashed upper part of my elbow (4-5 pieces). The xrays show full union. I wish the soft tissue were healing as fast but an olecranon osteotomy is a nasty procedure on the connective tissue. Sharing that because bone health has been a focus of mine for almost 3 years and most recently due to an accident. I wish I could get my wife to be disciplined to work on her bone health. I am also not implying that I know much of anything other than we can be much healthier as we age than presupposed.
https://www.frontiersin.org/articles...014.00137/full