You might believe that drinking milk, with all its calcium and vitamin D, is the one thing you need for strong and healthy bones. And it's a really nice message that sold a lot of milk over the years, but it's just not scientifically accurate.

你可能認為喝牛奶所攝取到的鈣和維生素 D，是強健骨骼所需要的。 這是個很好的廣告，使多年來販賣出了大量的牛奶，但在科學上並不夠精準。

When we focus on milk, we lose the bigger picture of bone health. So let's start at the beginning.

當視線只聚焦於牛奶時，我們失去了關注整體骨頭健康的能力，所以讓我們從頭開始。

Adults have 206 bones that form the main part of the skeletal system. They're the support structure or cage that protects our organs, but they do so much more. They work with our muscles to move our bodies, they store important minerals, they produce hormones, and they even make our blood.

多數成年人擁有206塊骨頭組成他們的骨骼系統，以形成支撐來保護內臟，但骨骼的作用不止於此。它們與肌肉配合使我們能夠活動，同時儲存著重要的礦物質，甚至於產生激素及血液。

Many people think of a Halloween skeleton when they imagine bone, but that only gives us a one-dimensional view. Bone actually has three layers.

提到骨骼，許多人腦海中浮現的是萬聖節的裝扮，但這只顯示了骨骼的表層。實際上骨頭有三層結構。

On the outside, there's the periosteum, a tough membrane that covers and protects. Next, there's a thick layer of compact bone, the white, hard, smooth part that most people are familiar with. But inside, there is spongy or trabecular bone, and an inner core filled with bone marrow, which contains stem cells that make blood and are constantly dividing.

最外層有著骨膜，一層包覆著的保護膜。接著便是緻密骨，也就是我們熟悉的白色堅硬且平滑的部分。但在裡面，是由骨小樑組成的海綿骨，以及包含造血幹細胞的骨髓。

Most people understand that our bones grow when we're kids and adolescents. We reach our peak bone mass in our 20s. What many people don't know is even after we stop growing, we are constantly removing old bone and replacing it with new.

大家都知道，我們的骨骼在幼年及青少年時期會生長，在20多歲時完成骨骼生長。但多數人並不知道，即使我們停止增長，但舊的骨頭會不斷地更新。

One estimate is enough bone is removed and replaced that a new skeleton is made every 10 years. After we reach our peak bone mass, bone removal starts to outpace replacement. This can eventually affect the integrity of the bone and it lowers the bone mass or the amount of bone that we have.

大約10年的時間，骨骼會完整的更新一次。當我們達到骨峰值一段時間後，骨量丟失速度會逐漸超過形成速度。這將會影響骨骼整體的完整性，且降低整體的骨量。

The bone disease osteoporosis is an extreme version of this process. Bone loss outpaces replacement, and combined with other changes, this can lead to so much fragility that even small bumps or falls can create fractures.

骨質疏鬆便是極端的例子，流失速度超過了形成速度，以及其他的因素，讓骨頭極為脆弱，即使小擦撞或跌倒，都有可能造成骨折。

Another cool fact about bones is they store calcium, so if intake is low, meaning not enough in our diet, the body draws calcium from the bone. This can also contribute to bone loss, so we need enough dietary calcium to maintain our bone. Vitamin D fits into the picture because it helps our body absorb calcium.

另一個有趣的事情是，骨頭中儲存著鈣，所以當攝入量不足時，身體會從骨頭中吸取鈣，而這導致了骨量丟失。所以必須攝取足夠的鈣來維持骨質。維生素Ｄ則可以幫助身體吸收鈣。

When we think of calcium and vitamin D, many of us picture a frosty glass of milk. Milk is not the only good source of calcium out there. Humans are creative omnivores. We can get calcium from a lot of other sources -- yogurt and cheese, for example -- but also look for leafy greens like spinach and kale, cruciferous vegetables like broccoli and cabbage, and proteins like tofu, nuts, beans, eggs and fish.

當說到鈣以及維生素Ｄ時，很多人腦中會浮現一杯玻璃杯，裡面有著冰涼的牛奶。牛奶並不是唯一的鈣來源，人類是富有創造力的雜食動物，我們還可以從很多來源中攝取鈣，例如優格和乳酪，或是可以尋找菠菜和羽衣甘藍這類綠葉植物、花椰菜或是甘藍這種十字花科的植物，以及豆腐、堅果、豆類、雞蛋、魚這類蛋白質。

Fortified cereals and orange juice are also good too, and chia seeds. And vitamin D is plentiful in fatty fishes, and our skin makes it from the sun. However, some people may need supplements.

加工過的穀物和橙汁也不錯，奇亞籽也是。維生素Ｄ則富含於豐富脂肪的魚類，以及日照產生，但總會有人需要補充。

Another important factor for bone health is exercise. Mechanical loading stimulates the cells that build bone and muscles pulling on the bone may do this as well. In fact, any activity that puts stress on your bones, like walking, jogging, dancing, racket sports, even strength training like doing weights, stimulates extra deposits of calcium and growth of new bone.

另一個影響骨骼健康的因子是鍛鍊，機械負荷跟肌肉拉動骨骼可以刺激建造骨骼的細胞。事實上，任何對骨頭施加力量的活動，健走、慢跑、跳舞、球拍類運動，甚至像舉重這類力量訓練，都會刺激鈣的儲存以及新骨骼的生長。

In addition, stronger muscles can help with balance. And one of the best ways to prevent a hip fracture? Reducing falls with better balance.

此外，強健的肌肉可以幫助平衡。而預防髖部骨折的最好方式之一是 ? 保持平衡來減少跌倒的可能。

If milk is your thing, that's completely OK, but don't forget that bone health is so much more than just milk.

如果你熱愛牛奶，完全沒有問題。但請記得，骨骼健康可不僅僅是牛奶。

額外補充

成骨細胞﹙osteoblast, OB﹚

骨形成的主要功能細胞，負責骨基質的合成、分泌及礦化。生產新的骨骼以及修復破碎的骨骼。

蝕骨細胞﹙osteoclast, OC﹚

分解骨骼，在骨頭形成空間容納血管和肌肉，分解舊的骨骼好讓他更新。

骨髓

分為紅骨髓及黃骨髓，紅骨髓能製造紅血球、血小板及白血球，黃骨髓主要是脂肪組織，某些情況下能轉變成紅骨髓。