【英语国际】美国将每日维生素D推荐摄入量提高两倍

A long-awaited report from the Institute of Medicine to be released Tuesday triples the recommended amount of vitamin D most Americans should take every day to 600 international units from 200 IUs set in 1997.

That's far lower than many doctors and major medical groups have been advocating -- and it could dampen some of the enthusiasm that's been building for the sunshine vitamin in recent years.

Many doctors have added blood tests of vitamin D levels to annual physicals, and sales of vitamin D supplements have soared to $425 million last year from $40 million in 2001, according to the Nutrition Business Journal.

It's long been known that vitamin D is essential to maintaining strong bones. But hundreds of new studies have also linked low vitamin D levels to a higher risk of a slew of chronic health problems -- heart disease, stroke, diabetes, prostate, breast and colon cancers, auto-immune diseases, infections, depression and cognitive decline. Studies have also suggested that many Americans are vitamin D deficient due to working and playing indoors and slathering on sunscreen.

The Institute of Medicine, an arm of the National Academy of Sciences that sets governmental nutrient levels, said there wasn't enough evidence to prove that low vitamin D causes such chronic diseases; it based its new recommendations on the levels needed to maintain strong bones alone.

'The evidence for bone health is compelling, consistent and gives strong evidence of cause and effect,' said Patsy Brannon, a professor of nutritional sciences at Cornell University and member of the IOM panel. For the other health problems, she said, 'there are relatively few randomized controlled trials, and even in the observational studies, the effects are inconsistent.'

The new recommendations, which cover the U.S. and Canada, call for 600 IUs daily for infants through adults age 70 and 800 IUs after age 71. The IOM assumed that most people are getting minimal sun exposure, given rising concern over skin cancer and latitudes where the sun is too weak to create vitamin D on the skin much of the year. The panel also raised the acceptable upper limit of daily intake to 4,000 IUs for adults, from 2,000 previously.

Those levels do take into account vitamin D from food sources -- but only a few, such as salmon and mackerel, contain much naturally. Milk fortified with vitamin D contains about 40 IUs per cup. Most Americans and Canadians need to get much of their vitamin D from supplements.

The IOM panel also issued new recommendations for daily calcium intake -- ranging from 700 milligrams for children aged 1 to 3 up to 1,200 milligrams for women 51 and older. The main change from the 1997 recommendations was to lower the recommended level for men 50 to 70 to 1,000 from 1,200. The panel noted that teenage girls may not get enough calcium, and that postmenopausal women may get too much, running the risk of kidney stones.

2010年11月30日，美国医学研究院(Institute of Medicine)发布了一份期待已久的报告，将绝大多数美国人每日维生素D的推荐摄入量提高两倍，从1997年的每日200个国际单位(IU)增加到每日600个国际单位。

Getty Images美国医学研究院还发布了钙的每日推荐摄入量——从1到3岁的儿童每日700毫克，一直到51岁以上女性每日1,200毫克不等。这一推荐摄入量比许多医生和主流医学组织提倡的服用量少得多，也给近年来人们对维生素D这种“阳光维生素”与日俱增的热情降了降温。

据《营养商业期刊》(Nutrition Business Journal)称，很多医生在每年的常规体检中加入了维生素D浓度测试的验血项目，维生素D片的销售额从2001年的4000万美元激增到2009年的4.25亿美元。

维生素D在维护骨骼强健方面的重要作用长期为人所知，但数百项新研究还将体内维生素D浓度过低与各种慢性病的患病几率挂起钩来——如心脏病、中风、糖尿病、前列腺疾病、乳腺癌、结肠癌、自身免疫类疾病、传染病、抑郁症和认知能力衰退等。研究还表明，许多美国人由于长期在室内工作娱乐以及大肆使用防晒霜，导致体内缺乏维生素D。

美国医学研究院是美国国家科学院(National Academy of Sciences)的分支机构，负责制定政府指导的营养摄入指标。该研究院称，还没有充分的证据可以证明维生素D浓度过低会导致慢性疾病，其新公布的每日维生素D摄入量是根据人体维持骨骼强健所需的维生素D水准来确定的。

康奈尔大学(Cornell University)营养学教授、美国医学研究院理事派西•布莱侬(Patsy Brannon)说，维生素D有益于骨骼健康的证据十分充分，具有一贯性，且因果关系明显。对其他疾病而言，随机对照临床研究相对较少，即使是在观察性研究中，维生素D的效果也不具备一贯性。

新的维生素D推荐摄入量将在美国和加拿大推广，建议从婴儿到70岁的成人每日服用600个国际单位，71岁以后的成人每日服用800个国际单位。美国医学研究院假设绝大多数人都获得最低程度的日光照射，因为过度暴晒可能导致皮肤癌的问题正得到人们的日益关注；此外，有些纬度的地方全年很多时间日照不足，无法通过人体皮肤产生足够多的维生素D。研究院还建议成人每日摄入的维生素D最多不超过4000个国际单位，比之前的2000个国际单位有所提高。

上述指标没有考虑从食品来源获得的维生素D。不过，只有三文鱼和鲭鱼等少数几种食品天然就含有较多的维生素D，添加维生素D的牛奶每杯含有约40个国际单位。大多数美国人和加拿大人都需要额外补充维生素D。

美国医学研究院还发布了钙的每日推荐摄入量——从1到3岁的儿童每日700毫克，一直到51岁以上女性每日1,200毫克不等。与1997年相关指标的主要不同在于，50到70岁男性的每日推荐摄入量从1,200毫克降至1,000毫克。研究院注意到，十几岁的女孩可能钙摄入量不足，而绝经后的妇女可能钙摄入量过多，导致肾结石的风险加大。