美国国立卫生研究院（The National Institutes of Health，NIH）每年在医学研究的投入近301亿美元。

美国外交官和政治学家亨利 基辛格（Henry Kissinger）曾指出，“因为风险小，学术政治是如此邪恶。”

For science — as for politics and economics — 2011 was a year of upheaval, the effects of which will reverberate for decades. The United States lost three venerable symbols of its scientific might: the space-shuttle programme, the Tevatron particle collider and blockbuster profits from the world's best-selling drug all came to an end. But the year also saw stirrings of science's future: hopes that research might blossom following the Arab Spring; cheap vaccines rolling out in Africa; and the first fruits of genome sequencing being used in the clinic. All this was overshadowed by the triple trauma of Japan's devastating earthquake, tsunami and nuclear meltdown, and a continual chipping away at science funding as nations struggled with the financial crisis.

维生素 D 是一种脂溶性维生素，具有抗佝偻病作用。维生素 D 家族有五种化合物，其中对健康关系较密切的是维生素 D2（以下简称「D2」）和维生素 D3（以下简称「D3」）。在化学结构上 D2 比 D3 多一个甲基和碳碳双键，另外两者来源、代谢产物也不同，D2 和 D3 均需要经过代谢产生活性物质来发挥作用。关于维生素