是比较tricky，VD缺乏症肯定有害健康，但到底多大剂量最好？

推荐量是在现有证据的基础上作出的。另外 600IU 的日补充剂量是假设基本没有日光照射，还包括了从日常饮食中摄取的VD。应该注意的是我们日常吃的一些食品里已经添加了VD，例如VD强化的牛奶、豆奶和橙汁。

给健康的成人补充更高剂量的VD？我觉得还是要谨慎一些，虽然的确有一些证据表明1000 IU 以上的日补充量可以起到防癌、防心血管疾病的效果(but not without controvercy)。

An example (from wiki),

A randomized intervention study involving 1,200 women, published in June 2007, reports that vitamin D supplementation (1,100 international units (IU)/day) resulted in a 60% reduction in cancer incidence, during a four-year clinical trial, rising to a 77% reduction for cancers diagnosed after the first year (and therefore excluding those cancers more likely to have originated prior to the vitamin D intervention). The study was criticized on several grounds including lack of data, use of statistical techniques and comparison with a self-selected (i.e. non-randomized) observational study that found long term convergence of breast cancer incidence  The author's response provided the required data, explained their statistical usage and commented that even if the vitamin D merely delayed the appearance of cancer (which they did not believe, based on other studies), that that was still a considerable benefit.