Knowing your vitamin D levels might not be as important as you think.
By
Julissa Treviño, Popular Science
In 2010,
The New York Times
called vitamin D the most talked-about supplement of the decade. Nearly
10 years later, the frenzy over the “sunshine vitamin” hasn’t died.
Last year, the
Times
reported that millions of people are taking a vitamin D supplement in
the hopes of curbing depression and fatigue, and even helping with
cancer.
“Vitamin D has been pretty hyped up,” says Monique Tello, a
physician at Mass General Hospital and a contributor to Harvard Health
blog. “It’s one of the vogue vitamins right now. It’s also controversial
among academics because there are two viewpoints on what healthy levels
of vitamin D are and how much we need it.”
So what does vitamin D
even do for the body, what’s the right amount, and who actually needs to
take a supplement? Here’s what you need to know.
What is vitamin D and what does it do?
[post_ads]Vitamin
D is a fat-soluble vitamin that helps promote the absorption of calcium
in the gut, says researcher and nutritional epidemiologist Francesca
Crowe of the University of Birmingham in England. When we ingest vitamin
D, our bodies convert it to calcitriol, the vitamin’s active form.
Calcitriol then prompts the body to produce a handful of proteins in the
gut whose job it is to transport calcium from the inside area of the
intestine, through its wall, and into the blood. As such, she says,
“vitamin D is very important for bone health.” Since calcium helps grow
and maintain strong bones,
studies have found that vitamin D deficiency can lead to bone diseases.
In
addition to healthy bones, there may be other health benefits to
vitamin D. For example, some studies have shown potential positive
impacts on
cardiovascular diseases,
and some experts suggest it can also lower rates of respiratory
infections in both children and adults. But these haven’t been
well-established, Crowe says.
Where should you be getting your vitamin D from?
According to the
Endocrine Society’s guidelines on vitamin D,
exposure to sunlight is the major source for children and adults. When
UV rays hit our skin, it triggers vitamin D synthesis by converting
7-dehydrocholesterol, which our skin naturally contains, to vitamin D3.
This molecule then travels through the liver and into the kidneys, where
it’s converted to calcitriol (the active formulation). Foods and
supplements can also provide this active type.
As the public’s
general awareness around sun damage and skin cancer has increased, the
number of people regularly using sunblock has also increased (this is
largely due to the invention of modern sunscreen
back in the 1970s
that led to its widespread use). As such, it may not be as easy to get
all of the vitamin D you need from the sun alone. According to a
2012 study,
wearing a sunscreen with SPF 30 does reduce the synthesis of vitamin D
by 95 percent. However, Tello says, in all likelihood, most people don’t
apply enough sunscreen, or re-apply as often as they should, for this
to be a true problem.
Tello says to get their recommended daily
intake of vitamin D, many people only need to expose their arms and legs
to the sun’s rays for between five and 30 minutes twice a week—though
this amount is likely higher for people with darker skin as melanin
blocks some of the rays.
This isn’t an invitation to lay out in
the sun, however. “Our body naturally makes vitamin D when the UVB rays
hits the skin, but UVB rays also cause skin cancer, so we want people to
cover up and still wear sunscreen,” says dermatologist Rebecca Baxt of
New York University’s School of Medicine. The
National Institutes of Health
(NIH) also notes: “There are no studies to determine whether
UVB-induced synthesis of vitamin D can occur without increased risk of
skin cancer.”
Unfortunately, few foods naturally contain vitamin
D. Those include oily fish like tuna, salmon and mackerel, eggs and cod
liver oil. Other foods, like orange juice, breakfast cereals and milk,
are fortified with vitamin D in many countries.
Sure enough, evidence shows that diets really do impact our vitamin D levels. In a
2011 study
testing how different diets—meat-eating, fish-eating, vegetarianism,
and veganism—impact vitamin D levels, Crowe found that vegans had lowest
levels of blood vitamin D.
Some people may also need to take a supplement, though not everyone should.
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What’s a “healthy level” of vitamin D?
That’s
the million dollar question and it remains disputed even among experts,
with medical organizations having different estimations for “healthy”
vitamin D levels. One reason for this ambiguity is that interest in the
vitamin is relatively new. “We’ve only been able to easily measure blood
levels of vitamin D for about 15 years ago”, Tello says. In that time,
we still haven’t established a healthy level.
For example, according to a
2010 report
issued by the Institute of Medicine, adults with a blood level of 20
ng/mL were considered vitamin D deficient; they figured that this, or
more, is the amount of vitamin D needed for good bone health. Meanwhile,
the Endocrine Society’s
2011 clinical practice guidelines
suggested that a higher level—at least 30 ng/mL but preferably 40 to 60
ng/mL “to guarantee sufficiency”—is needed based on the expert advice
of their “Vitamin D Task Force.”
Tello says she feels that between
20 and 30 ng/mL is a safe bet. For most people who “have a varied diet
and they get a little bit of sun, it isn’t hard to be in this range.”
Because
most people might not be checking their blood levels, some
organizations and countries have adopted more specific intake
recommendations. For example, the U.S. Institute of Medicine suggests a
daily intake of 400 to 800 international units, or 10-20 micrograms, for
most healthy adults. (Tello says most vitamin D supplements offer 600
or 800 international units daily.)
The UK also recommends 10
micrograms of vitamin D each day, particularly in the form of a
supplement, Crowe says. “It’s a small amount, but it’s actually quite
difficult to get vitamin D from your diet,” she says. “You’d have to eat
oily fish every day, but you shouldn’t, because of the risk of mercury
and things like that.”
Who’s at risk of vitamin D deficiency?
Several
factors play into whether you’ll become deficient, Crowe says. Some
populations are more at risk, including the elderly, who spend less time
in the sun, and those with illnesses who are housebound because they’re
not getting enough sunlight; people with darker skin (because the
melanin reduces the amount of UVB rays to hit the skin); people who
cover up a large portion of their skin, such as for religious purposes;
and people who have problems with calcium absorption, like those with
celiac disease, because they can’t absorb vitamin D as well.
“These groups should be taking a supplement,” Tello says. The
2005 Dietary Guidelines for Americans also called on high-risk groups to consume 25 micrograms of vitamin D.
Sunscreen,
cloud cover, and pollution can also affect how much sunlight you get,
so those who live in cities that don’t get much sun could also be at
risk, Crowe says.
What happens when you’re deficient?
[post_ads]Not
getting enough vitamin D can result in some serious—and
scary—consequences. In children, a deficiency means “they aren’t able to
absorb calcium well enough,” Crowe says. In children, unless they
aren’t spending anytime in the sun, a deficiency usually results from
their bodies not being able to absorb the stuff properly. This can lead
to rickets, a condition first described in the 17th century in which
bone tissue fails to properly mineralize, resulting in soft, weak bones
that can be easily fractured and deformed.
By the 1930s, rickets
had become a rare disease in the United States after the U.S. government
began fortifying the nation’s milk with the necessary vitamin. But some
children remain at risk. Rickets has been linked to babies whose moms
exclusively breastfeed them but the mothers themselves are vitamin D
deficient, often from excessive sunscreen use. It’s also been found in
children whose daycare programs don’t have much outdoor activity and it
can even be the result of genetic differences, according to the NIH.
A
growing number of children in the U.K. have experienced the condition
in recent years, Crowe says. “That’s mainly because there’s been more
immigration,” she says. “People with darker colored skin have to expose
their skin to the sun for longer than someone with light colored skin to
get the same vitamin D.” She says it frequently occurs when people who
have darker skin move from a place with lots of sunlight to one with far
less.
In adults, a similar condition called osteomalacia that
results in weak bones,can develop from low vitamin D. Tello says this
condition has also been linked to osteoporosis. Rickets and osteomalacia
are reversible with treatment of prescription-strength vitamin D
supplements.
Anecdotally, low vitamin D levels have also been
linked to fatigue, seizures, and changes in the heart muscle. But
there’s not enough data or studies to determine how low your vitamin D
levels need to go, or if other factors are involved.
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Can you have too much vitamin D?
While
naturally-derived sourcing of vitamin D isn’t bad for you—the body, in
fact, controls how much vitamin D you get from the sun and food and can
store it for winter—there are real dangers associated with taking too
much of the supplement.
The Times’ Gina Kolata
reported last year that some people “are taking supplemental doses so high they can be dangerous, causing poor appetite, nausea, and vomiting.”
Tello
says she’s experienced this in her practice as well. “I’ve seen
patients who’ve taken that supplement daily because they thought they
were doing something good for themselves.” Moderately high levels of
calcium, as a result of high vitamin D levels, over a long period of
time can lead to abdominal pain, peeing frequently, and kidney stones;
this can even weaken your bones. “People may be feeling these things and
not know why.”
Should you be screened for vitamin D levels?
Vitamin
D testing is not currently part of any kind of panel of routine exams,
and most people need not worry, or even be tested, Tello says. In a 2014
recommendation from the U.S. Preventive Services Task Force published
in
Annals of Internal Medicine, a panel agreed: Most people don’t even need to know their vitamin D level.
Tello
is hopeful that the medical community will come to a consensus on
recommended blood levels for different groups of people. That way, we
can all get the proper amount of sunshine (or necessary supplement) we
need.
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