健康生活:補鈣須謹慎 過量有風險大綱

While many people aren't getting enough calcium, new research cautions that some people may have the opposite problem: They could be getting too much.

儘管有很多人鈣攝入量不足，但新的研究提醒我們，也有一些人面臨的問題可能恰好相反：他們的攝入量太多了。

Americans spend more than $1 billion a year on calcium supplements in hopes of staving off osteoporosis, the brittle bone disease that cripples many elderly women and some men.

美國人一年花費逾10億美元購買各類鈣補充劑，期望能推遲骨質疏鬆症的發生。骨質疏鬆症是一種讓骨頭變脆的疾病，許多老年女性和部分男性都會因骨質疏鬆致殘。

Yet recent studies link calcium supplements to a higher risk of heart attacks and kidney stones. Last month, the U.S. Preventive Services Task Force issued a draft recommendation against taking calcium and vitamin D, saying there wasn't enough evidence of benefit to justify the risk.

但近期的研究揭示，鈣補充劑有可能導致心臟病和腎結石風險升高。美國預防醫學工作組(U.S. Preventive Services Task Force)上月發佈了一份建議書草案，不主張服用鈣和維生素D補充劑，稱並沒有充足的證據顯示這樣做利大於弊。

For generations of Americans who grew up exhorted to drink their milk to maintain strong bones, the reports raised troubling questions: Is calcium not so important after all? Are the supplements unsafe? And how much is too much?

對從小就被勸說要多喝牛奶以維持強健骨骼的幾代美國人來說，這些報告引發了一些麻煩的問題：鈣是不是其實並不太重要？鈣補充劑是不是不安全？攝入鈣量多少算超量？

'It's gotten very confusing but it doesn't need to be,' says Ethel Siris, director of the Toni Stabile Osteoporosis Center at Columbia University Medical Center in New York.

紐約哥倫比亞大學醫學中心(Columbia University Medical Center)託尼•斯塔比爾骨質疏鬆研究中心(Toni Stabile Osteoporosis Center)主任西里斯(Ethel Siris)說，“問題變得令人非常費解，但其實不至於如此。”

The links to heart attack and kidney stones involved calcium supplements, not calcium from food sources, Dr. Siris and other experts note. Many other studies have not found such health risks, so more research is needed to understand what levels, if any, might be hazardous.

西里斯博士和其他專家指出，可能引起心臟病和腎結石的是鈣補充劑，而不是從食物中獲取的鈣。許多其他研究並未發現這類健康風險，因此，若要了解鈣攝入量過多是否會有危險以及達到多少可能會有危險，還需要做更多研究。

Meanwhile, experts say they are still more concerned that too many Americans aren't getting enough calcium, since the body can't make it on its own.

專家們同時也說，他們更擔心的仍然是有太多美國人鈣攝入量不足，因爲人體無法自己製造鈣。

'Unless you take in enough calcium, by mouth, every day, you have to keep borrowing it from your skeleton, so over your lifetime, you need to get enough,' says Dr. Siris. 'If you have low bone mass, or are at risk for fractures, you want to minimize any need to take calcium from the skeleton.'

西里斯博士說，“除非每天都能經口服攝入充足的鈣，否則你不得不一直向骨骼借用鈣，所以人一生中必須攝取足夠的鈣。如果你骨密度低，也就是說有骨折風險的話，你就得儘量避免從骨骼中獲取鈣。”

How much calcium people need varies by age and gender. Adults generally need 1,000 milligrams daily, rising to 1,200 mg for women over 50 and men over 70, according to guidelines issued in 2010 by the Institute of Medicine, an independent advisory group. Children need 1,300 mg daily during the peak growing years of 9 to 18.

人體需要的鈣量依年齡和性別而有不同。根據獨立顧問組織藥學研究所(Institute of Medicine)2010年發佈的指導原則，成年人一般需要每天攝入1,000毫克鈣，50歲以上的女性和70歲以上的男性每天需要攝入的鈣量會增加到1,200毫克。孩子在九到18歲的生長高峯期每天需要1,300毫克鈣。

People also need sufficient levels of vitamin D to absorb the calcium. The IOM recommends 600 international units a day for most adults, and 800 daily after age 70, although many physicians recommend more. It is difficult to take in that much vitamin D from food sources, and prolonged sun exposure, the best source of vitamin D, can lead to skin cancer, so experts say many people should take vitamin D in supplement form.

人體要吸收鈣，還需要攝取充足的維生素D。藥學研究所建議多數成年人每天攝入600國際單位的維生素D，並建議70歲以上的人每天攝入800國際單位，不過許多醫生推薦的攝取量要大於這個數。從食物中攝入這麼多的維生素D很難，而長時間陽光照射（維生素D的最佳來源）可能導致皮膚癌，因此專家稱，許多人都應該服用維生素D補充劑。

Getting adequate calcium from food is easier. For example, 8 ounces of milk or 6 ounces of yogurt has 300 mg of calcium, and one cup of spinach has 270 mg. But studies show on average, Americans get only about 750 mg of calcium from their diets.

從食物中獲取充足的鈣則比較簡單。比方說，八盎司牛奶或六盎司酸奶中含有300毫克鈣，半品脫菠菜中含有270毫克鈣。但研究顯示，美國人平均只能從食物中獲得約750毫克鈣。

Many of the more than 30 million Americans who are lactose intolerant don't get

逾3,000萬乳糖不耐受的美國人無法獲得充足的鈣，或者要依賴鈣補充劑。

'For people who can't or won't get more in their diet, it's better to fill that gap with supplements than to stay on the low side,' says Bess Dawson-Hughes, director of the Bone Metabolism Laboratory at the USDA Nutrition Center at Tufts University. 塔夫茨大學(Tufts University)美國農業部營養中心(USDA Nutrition Center)

骨骼新陳代謝實驗室(Bone Metabolism Laboratory)主任道森休斯(Bess Dawson-Hughes)說，“對無法或沒能通過飲食攝取更多鈣的人來說，用營養片劑來補鈣比缺鈣要好。”

Consuming too little calcium can contribute to osteoporosis, a thinning of the bones that causes more than 2 million fractures a year. Once osteoporosis sets in, taking extra calcium and vitamin D won't prevent fractures. But not getting enough of the nutrients can make bone loss worse.

攝入鈣量過少會引起骨質疏鬆，骨質疏鬆症導致每年逾200萬例骨折事件發生。一旦得了骨質疏鬆症，即使攝入額外的鈣和維生素D也無助於防範骨折。但如果這些營養物質攝入不足的話，骨耗損會加重。

On the other hand, it is easy to consume more than the 2,000 mg a day that the IOM considers the safe upper limit for adults. 'A number of health-care providers say, 'Oh, the requirement is 1,200 mg daily, so take 1,200 mg in supplements,' regardless of what the patient is consuming in food,' says Dr. Dawson-Hughes. 'If you have a bowl of Total in the morning and a yogurt and a glass of milk for lunch, you can get to 2,000 mg easily.' Multivitamins also contain calcium in widely varying amounts. Chewable chocolate, caramel and gummy-bear varieties have made calcium supplements as appealing as candy.

從另一方面來說，人一天的鈣攝入量很容易超出2,000毫克（被藥學研究所視爲成年人的安全上限）。道森休斯博士說，“許多醫療服務機構會說，‘哦，一天必須攝入1,200毫克鈣，所以要服用1,200毫克補充劑，’他們不管患者吃的是什麼樣的飲食。如果你早晨喝一碗Total牌穀物片，中餐喝一盒酸奶和一杯牛奶的話，很容易就能攝入2,000毫克鈣。”複合維生素片中也或多或少地含有鈣。鈣補充劑能製成可以嚼着吃的巧克力、太妃糖和小熊糖等品種，像糖果一樣吸引人。

In general, any vitamins or minerals the body can't absorb are simply excreted. But studies linking calcium supplements to heart attack and kidney stones have made experts more wary of excess calcium than before.

總體而言，任何人體無法吸收的維生素或者礦物質都會被排泄出去。但由於研究發現鈣補充劑與心臟病和腎結石存在關聯，專家們對過量攝入鈣這一問題比從前更加警惕。

In a 2006 report from the Women's Health Initiative, a large government study, women who took 1,000 mg of calcium daily had 17% more kidney stones than those who got a placebo. But subjects were allowed to eat their usual diet, and take calcium supplements on their own, no matter what group they were in, so their total calcium intake was unknown.

大型政府研究項目“婦女健康倡議”(Women's Health Initiative)2006年的一份報告顯示，每日服用1,000毫克鈣補充劑的女性患腎結石的風險比服用安慰劑的女性高17%。不過在此項研究中，兩個組別的實驗對象都被允許按照她們的日常飲食習慣來吃東西，鈣補充劑也是自行服用，因此她們攝入的鈣的總量是未知的。

In the 12-year Nurses' Health Study of 90,000 women, those who consumed a high level of calcium in food had fewer kidney stones than those who consumed less.

爲期12年的“護士健康研究”(Nurses' Health Study)對九萬名女性進行了研究，研究發現，從飲食中攝取大量鈣的女性患腎結石的風險要低於鈣攝入量較少的女性。

Studies linking calcium intake and heart-attack risk are similarly confusing. A study of 24,000 Germans published in the journal Heart last month, found that those who consumed about 820 mg of calcium a day had a 31% lower risk of heart attack than those who consumed much less. But those who got their calcium exclusively from supplements were more than twice as likely to have a heart attack as those who took no supplements.

揭示鈣攝入量與心臟病風險之間關聯的研究也令人感到有些困惑。《心臟醫學期刊》(Heart)上月刊登了一項針對24,000名德國人的研究，研究發現，每日攝入約820毫克鈣的人患心臟病的風險比攝入量少得多的人低31%。但僅從補充劑中攝取鈣的人患心臟病的風險則比不服用任何補充劑的人高出一倍以上。

In 2010, researchers in New Zealand analyzed 11 clinical trials involving 12,000 people, and found that those taking calcium supplements had a 30% higher risk of heart attack than those who didn't. However, the studies didn't include people taking vitamin D, which some researchers believe is protective for the heart.

2010年，新西蘭的研究人員對涉及12,000名試驗對象的11項臨牀試驗進行了分析，發現服用鈣補充劑的人患心臟病的風險比不服用鈣補充劑的人高30%。然而，相關研究未將服用維生素D的人包括在內，一些研究人員認爲，維生素D可保護心臟。

Exactly how calcium supplements might contribute to heart attacks baffles cardiologists. 'Nobody has associated the calcium in your bloodstream with calcification in your arteries,' says Nieca Goldberg, medical director of the Joan H. Tisch Center for Women's Health at New York University Langone Medical Center. Still, she says she now urges patients get their recommended calcium from food than from supplements to avoid possible problems.

鈣補充劑究竟是怎麼導致心臟病呢？這個問題令心臟病學家疑惑不解。紐約大學朗格尼醫學中心(New York University Langone Medical Center)瓊•H•蒂施女性健康中心(Joan H. Tisch Center for Women's Health)的醫學主任戈德堡(Nieca Goldberg)說，“沒有人發現血液中的鈣與動脈血管鈣化有什麼聯繫。”不過，她說她現在會敦促患者通過膳食而非補充劑來攝取推薦量的鈣，以避免潛在風險。

Osteoporosis experts also urge patients not to take more than the recommended amount of calcium. 'Women should definitely stop taking two big calcium supplements a day,' says Dr. Dawson-Hughes. Even if the risks remain unclear, taking more than the body can absorb doesn't benefit bones, 'so it's not worth any risk -- real, imaginary, uncertain, possible or probably,' she adds.

骨質疏鬆症專家也敦促患者不要攝取超過推薦量的鈣。道森休斯博士說，“女性肯定不應該再一天服用兩大片鈣補充劑了。”即使相關風險我們還不清楚，但攝入超過身體吸收能力的鈣對骨骼沒有好處，她還說，“所以不值得去冒險──不管是真正的、想象的、不確定的、有一定可能的還是可能性很大的風險。”