To resolve controversy over how much vitamin D is enough to protect older adults’ health, researchers tested Cardiovascular Health Study blood samples. They sought links between each person’s 25 (OH) D and first heart attack, cancer diagnosis, hip fracture or death. Risks rose when levels fell below 20ng/mL or 50 nmol/L. Results match the low threshold level set by the Institute of Medicine. Association with risk varied seasonally. Levels were lower, and disease event risk higher, in winter.