The recommended dosage is 800~1000 U/d of plain vitamin D for healthy old people and up to 2000 U/d for people with osteoporosis, obesity, poor sun exposure, and malabsorption.

推荐老年人每天补充800~1000 U普通维生素D，骨质疏松患者、肥胖、缺乏日照和吸收不良的人可酌情增加至2000 U。

youdao

The Institute of Medicine, which advises the U.S.government on health, is expected to update its recommended amount of vitamin D by September.

VOA: standard.2010.05.28

"Vitamin D has become a very hot topic in medicine now as we are discovering very high levels of vitamin D deficiency in our population, not only in the U.S.,but worldwide" Vitamin D helps our bodies absorb calcium and helps form and maintain strong bones.

VOA: standard.2010.05.28

In the U.S. vitamin D levels are usually reported with a different measure using nanograms per milliliter.

WSJ: Swedish Study Links Multiple Sclerosis to Vitamin D Levels

The Selenium and Vitamin E Cancer Prevention Trial involving 35, 000 U.S. and Canadian men was halted in October when researchers determined that selenium was not protecting the men from prostate cancer and may have been causing diabetes in some of them.

CNN: Group threatens suit over vitamins' anti-cancer claims

In winter, experts say, people in the northern half of the U.S. don't receive enough UVB rays from the sun to make vitamin D, regardless of whether they use sunscreen.

WSJ: Swedish Study Links Multiple Sclerosis to Vitamin D Levels