Researchers from Wake Forest University School of Medicine in Winston-Salem, North Carolina, recruited 976 people aged 65 or older from two towns in the Chianti area of Italy. Scientists measured physical performance including walking speed, ability to stand up from a seated position, ability to maintain balance in several increasingly difficult postures and hand grip strength. Those who had low levels of vitamin D scored 5% to 10% lower in physical performance tests and hand grip strength than those with higher levels. Research does not show that low vitamin D levels cause poor physical performance, but doctors noted that muscles need vitamin D to function properly.
Separately, medical experts from Harvard Medical School have recently concluded that the optimal level for vitamin D begins at 75 nanomoles per liter of blood (nmol/L). In the Chianti study, nearly 75% of women and 51% of men had insufficient levels of vitamin D, meaning 50 nmol/L or less. Approximately 29% of women and 14% of men were deficient in vitamin D, which doctors classified as 25 nmol/L or less. Harvard researchers stated that the average adult would require 560 IU of vitamin D per day to raise the level by 10 nmol/L.
The U.S. Department of Agriculture currently recommends 200 IU of vitamin D per day for those under 50, 400 IU per day for those 50 to 70, and 600 IU per day for those over 70. There is a growing consensus in the medical community that vitamin D is safe at higher levels, that many people are deficient or insufficient in vitamin D and that the government should raise its recommendations.