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There are two forms available for vitamin D
维生素D补充剂，有两种形式
supplements; D2, ergocalciferol and D3,cholecalciferol.
分别是维生素D2和维生素D3
Vitamin D2 is made by the conversion of a sterol
维生素D2由植物和酵母的固醇转化而来
found in plants and yeast. Vitamin D3 is the form
维生素D3
that is produced naturally in human skin
是人类皮肤暴露在紫外线B光下自然生成的
exposed to ultraviolet B light and occurs
在某些动物产品中也存在，例如鱼肝油
in some animal products such as cod liver oil
在多脂鱼中也存在少量维生素D3
and in smaller amounts in other fatty fish
例如沙丁鱼和金枪鱼
such as sardines and tuna. Vitamin D3 is
维生素D3
the most common form used in dietary supplements
在膳食补充剂和牛奶等强化食品中
and fortified foods such as milk. Unlike calcium
是最常见的
these two forms are not equal in absorption.
与钙不同的是，维生素D3和D2两种形式的
Vitamin D3 is metabolized differently than D2
吸收效果是不同的，研究表明
and research shows it is more effective in
在提高活性型维生素D的血清浓度方面
raising serum concentrations of the active
D3要比D2更加有效
form of vitamin D and is also able to maintain
而且能够更加长久地使维生素D保持高水平
high levels for longer. More research is needed
这个领域还需要做更多的研究
in this area but many companies are switching from D2
但是很多企业，将D2的生产转向D3
to D3 to gain greater benefits from their supplements.
从而在钙补充剂中获得更多的利润
Let's take a minute to understand how to
下面,让我们了解一下
calculate the amount of vitamin D and calcium
如何通过食物的营养成分标签
provided in a food from the nutrition label.
计算维生素D和钙的总量
One serving of cheerios is equal to
一份麦片相当于一杯麦片粥
one cup of cereal. The nutrition label
麦片的营养标签包括
includes data for cereal alone and for the cereal
麦片单独的营养数据
with half a cup of skim milk because
也包括麦片与半杯脱脂牛奶共同的营养数据
it is typically consumed with milk. So be sure
因为麦片通常与牛奶一起食用
to understand which column you are reading.
所以一定要弄清楚你看的是哪一列
One serving of cereal alone has 100 calories.
一份麦片有100卡路里的能量
The cereal provides 10% of our
麦片为我们提供了
daily value of calcium. In order to determine
每天所需钙含量的10%
how many milligrams of calcium that provides
为了弄清楚麦片提供钙的数量
you need to know that the daily value for calcium
你需要知道人体每日所需要的钙
is 1000 milligrams. Once you have that information
是1000毫克，有了这个信息后
you can calculate how many milligrams in the serving
用1000乘以0.10或者10%
by multiplying 1000 milligrams by 0.10 or 10%.
你可以计算出每份麦片含有多少钙
The result is 100 milligrams of calcium
结果是每份麦片提供100毫克的钙
per serving of cheerios. Similarly a serving
同样的,一份麦片提供给你
of cheerios provides 10% of your daily value
每日所需钙含量的10%
of vitamin D. The daily value for vitamin D
每日所需维生素D为400IU
is 400 IU. To calculate the amount in a serving
想计算出每一份麦片提供多少维生素D
multiply 400 by 0.10. The result is 40 IU of
就用400乘以0.10
vitamin D per serving. To find
结果就是每一份提供40IU
a full list of daily values for all nutrients
想找到所有营养物质的每日所需含量
you can go to the FDA website shown
你可以登录屏幕一边FDA网址
on the side and search for daily values.
来搜索每日食物摄取量
Vitamin D plays important roles in many processes
维生素D在人体的很多程序上
throughout the body. Probably the most
都发挥着重要作用
well understood function that vitamin D has is in
最为人们所熟知的功能
the absorption of calcium from the small intestine.
就是它帮助小肠吸收钙
When vitamin D is inadequate calcium from the diet
当维生素D不足的时候
is poorly absorbed. Another well characterized
膳食中的钙就很难被吸收
and important role of vitamin D is to maintain
维生素另一个特别而重要的作用就是
appropriate levels of calcium and phosphate
保持血液中钙和磷酸盐的适当水平
in the blood to ensure proper bone formation,
进而保证正常的骨生成，骨骼矿化
mineralization, growth and repair. Vitamin D
骨生长和骨修复
has other roles that have been less well characterized.
维生素D还有其他不为人所知的作用
