The questions is: “I spend most of my winter days indoors, and when I’m outdoors, I’m covered from head to toe. If I only get a few minutes of sun exposure on my face and hands each day, is that enough to get adequate vitamin D? And if not, what should I do?”
اضافة اعلان
If you live in a country where winters are cold and gray, it
is smart to think about how you will get vitamin D — often called the
sunshine vitamin — over the next several months.
Vitamin D is synthesized in the skin after exposure to the
sun’s ultraviolet B rays, and is crucial for calcium absorption and the
maintenance of strong, healthy bones, said Julie Stefanski, a registered
dietitian nutritionist and spokeswoman for the Academy of Nutrition and Dietetics.
Deficiencies, which are common worldwide, can cause
soft, weak, and brittle
bones, leading to fractures. Your vitamin D status can also play a role in
other aspects of health including inflammation, autoimmune disease risk, heart
health and cognitive function.
Most healthy people with fair skin can typically produce
enough vitamin D during the summer by exposing their faces, arms and legs to
sunlight for about five to 10 minutes several times per week during midday,
when the sun is highest and its UVB rays are most powerful, said Antony Young,
an emeritus professor of experimental photobiology at the St. John’s Institute
of Dermatology at King’s College London, via email. (People who have more
melanin, or darker pigmentation, in their skin need longer periods in the sun
because melanin reduces vitamin D synthesis.)
The winter sun, however, does not have the same effect if
you live in regions north of the 37th parallel. In these places during the
cold-weather months (around October or November through April or March), the
sun is lower and its UVB rays are weak.
“Winter sunlight does not have enough of the UVB component
that is essential for vitamin D synthesis,” Young said. “For all practical
purposes, one cannot make vitamin D in cold climates in winter.”
That does not mean, however, that you cannot meet your
vitamin D needs during the chillier months. “You don’t need to get it from
sunshine,” said DrDeborah S. Sarnoff, president of The Skin Cancer Foundation
and a clinical professor of dermatology at the NYU Grossman School of Medicine.
How much vitamin D do you need?There is a lot of
controversy about how much vitamin D you
should have in your blood for optimal health, Young said. But in general, he
added, most major medical organizations recommend at least 20 nanograms per
milliliter as measured by a simple blood test.
How much vitamin D you should get from foods or supplements
is also debated, Stefanski said, noting that it’s difficult to suggest one
blanket recommendation for everyone. Your skin color, age, health conditions,
and sun exposure during warmer months, among other things, will influence how
much vitamin D you need each day.
Still, federal guidelines recommend that in general, to
maintain good bone health and normal calcium metabolism, people between 1 and
70 years of age should get 600 international units (or 15 micrograms) each day
— from foods, supplements or both. Those over 70 should get 800 IU (or 20
micrograms), according to the guidelines, and infants up to 12 months need 400
IU (or 10 micrograms).
“But many organizations don’t feel those numbers are high
enough,” Stefanski said. For example, the Endocrine Society — which recommends
a blood level of 40 to 60 nanograms per milliliter — says that most adults can
safely take between 1,000 to 2,000 IU (or 25 to 50 micrograms) of vitamin D per
day from either supplements or a combination of food and supplements.
If you are concerned about a
deficiency, are at risk for
osteoporosis or have a condition that affects how you absorb nutrients, talk
with a health care provider about getting your vitamin D level tested.
How to get vitamin D without the sunWhile winter’s chill is in the air, you will likely need to
look beyond the sun to satisfy your vitamin D needs, Young said.
Foods that supply the highest amounts of naturally occurring
vitamin D include fatty fish (such as salmon, tuna and sardines), cod liver
oil, beef liver, egg yolks, and some mushrooms. But because the typical
American diet tends not to include many or enough of those foods, manufacturers
have been fortifying foods with vitamin D since the 1930s. Good sources of
vitamin-D-fortified foods are cow’s milk, soy milk, cereal and orange juice.
Keep in mind, though, that it can be challenging to get enough vitamin D from
food sources alone, Stefanski said. And not all dairy products are fortified
with vitamin D, so make sure to check the nutrition facts label.
“Especially as we’re entering the
winter months,” Stefanski
said, “most people would benefit from taking a supplement.”
When looking for a supplement, choose vitamin D3 over
vitamin D2, Stefanski said, since research suggests you can absorb it more
effectively. Also, look for a supplement that has the USP Verified Mark on the
bottle, which indicates that the product contains the ingredients listed on the
label and does not contain harmful contaminants.
Just do not take more vitamin D than is recommended by the
packaging or your health care provider, Stefanski added. In excess, vitamin D
can build up in the body and lead to toxicity, which can result in symptoms
such as fatigue, weakness, confusion, vomiting, dehydration, constipation and
pain.
Another thing to avoid in your pursuit of
vitamin D, Sarnoff
said: the tanning salon. Not only do the machines increase your risk of skin
cancer, they also emit primarily ultraviolet A rays, which do not spur the skin
to make vitamin D. So stick with supplements and foods as your vitamin D
sources in the winter, and consider adjusting your strategy when the summer sun
returns.
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