Tag Archives: Vitamin D

Vitamin D and…food allergies?

Vitamin D deficiency: The root of all evil?

When I started writing posts about vitamin D, I thought it would be a straightforward three-part series: What does vitamin D do? What happens when you’re deficient in it? How can we prevent that from happening? The more I read on the subject, though, the more interesting things I learn—all of which underscore the need to supplement infants with vitamin D.

This latest item is from Australia—where they get plenty of sunshine—and turned up an association between vitamin D deficiency and food allergies in infants. Children in the Melbourne area with documented vitamin D deficiency were nearly four times more likely to suffer from food allergies than were those with normal vitamin D levels.

This supports the work of a number of researchers (one example here) who have found that people who live farther from the equator (and hence get less sunshine—and thus less vitamin D) are more likely to end up in an emergency room or hospital with a severe food allergy reaction than those who live in the tropics.

Sunshine and food allergies! That would have sounded like science fiction back in my 1970s med school days.

More on the relationship of vitamin D and immune system function coming up…


Filed under Allergies, Nutrition

Vitamin D (Part 2): Where do we get it?

Okay, now for a bit more detail about Vitamin D. In this post we’ll look at where it comes from, and how we get it to where it’s needed in the body.

1) Vitamin D metabolism

There are actually two forms of vitamin D: vitamin D2, which is synthesized by plants,  and vitamin D3 (cholecalciferol), which is synthesized by mammals, including us. This review will focus on D3, since that’s the most important form for humans.

There are two ways that humans get their daily vitamin D: sunshine (the most effective way) and diet.

Not exactly true...

First let’s clear up a common vitamin D misconception. We do not get vitamin D directly from the sun–that is, there are no tiny “Ds” raining down on us while we sunbathe by the pool. Rather, sunlight acts on a cholesterol-based vitamin D precursor our bodies make and converts that to previtamin D  in the skin. Previtamin D is then converted to vitamin D3 by the heat of the skin.

That’s just the beginning…

Once it leaves the skin, vitamin D3 jumps on board a specialized protein that transports it to the liver, where it’s converted to 25-hydroxyvitamin D (25-OH-D). From there 25-OH-D surfs to the kidneys on another specialized protein where, through the mysteries of biochemistry, it transforms itself into 1,25-dihydroxyvitamin D (1,25-OH2-D), the most biologically active form of vitamin D. Then it’s off to the tissues of the body to work some magic.*

We can also get vitamin D from what we eat, though D isn’t distributed very well in natural foods. Vitamin D-rich foods include oily fish like salmon and swordfish, and egg yolks, butter and liver (Liver!! My Gram Sloan, a big chicken liver fan, was right…). Vitamin D is added to milk nowadays, of course, but even so, unless you’re a traditional Eskimo–eating a lot of fish, seal and whale blubber–it’s unlikely that your daily diet provides more than half of your vitamin D needs.

2) Sunshine: How much is enough?

Many factors go into determining how much sun exposure we require to ensure a healthy level of vitamin D in the bloodstream. Time of year, latitude, skin pigmentation, weather, air pollution, clothing and sunscreen all play a role. Basically, a fair-skinned, sunscreen-free person getting 10-15 minutes of total body exposure during the summer months will produce about 10,000-25,000 international units (IU) of vitamin D in 24 hours. So a Celtic-skinned person (such as myself) living in a nudist colony on the equator (not gonna happen) would do just fine, vitamin D-wise, from sunshine alone…until the skin cancer gets him, that is.

But all those other factors, from clothing to clouds, literally get in the way. Take the simple factor of skin pigmentation: it can take 5 to 10 times more sunlight for a dark-skinned individual than a light-skinned one to produce the same amount of vitamin D. Consider the plight of, say, a Nigerian-born child living in

On the lookout for vitamin D...

Canada. Between the short northern winter days, cold-weather clothes and dark skin, the chances of getting enough vitamin D from sunshine are pretty remote.

And that’s true of just about everyone in the United States today, too, regardless of skin pigmentation. In a 1989 study on indoor air quality, the Environmental Protection Agency estimated that the average American spends 93% of his or her time indoors. Today, with computers, electronic games, and 600 TV channels to choose from, that sun-less percentage has likely increased, to the detriment of our vitamin D stores.

So, most of us are not getting nearly enough vitamin D from sunshine or diet. What potential impact does that have on our health?

Stay tuned…

* * *

*(Vitamin D metabolism, which involves skin, liver, kidneys, bowel, bones, sunlight, diet, heat, several specialized proteins and dozens of specific chemical reactions–and which can be disrupted by things like rainy weather, or how often you wear a hat outdoors–is not a good argument for intelligent design.)


Filed under Nutrition, Science

FAQs: Is Vitamin D necessary for breastfed babies? (Part 1)

This is the first in a series of frequently asked questions I hear from parents in my practice. If you have an FAQ about children’s health, send it along!

Vitamin D: A buffness requirement

Is vitamin D supplementation really necessary for breastfed babies?

Vitamin D supplementation for breastfed newborns is a hot topic. Though it’s strongly recommended by the American Academy of Pediatrics, many parents understandably question the need for it. After all, isn’t breast milk nature’s perfect food? Aren’t we undermining breastfeeding promotion by saying mother’s milk is deficient in something? And, hey…if this is such a problem, how did the human race manage to get by without vitamin drops all these eons??

Let’s look at the issue from a number of angles and see what the fuss is all about. I’ll start with a basic Q & A and then go into more detail in future posts.

1) What is vitamin D?

Vitamin D is a steroid hormone. It belongs to the same chemical family as cholesterol, testosterone and estrogen, among many other compounds.

2) What does vitamin D do?

It was originally thought to only play a role in bone health, by helping the body absorb calcium. In recent years, though, vitamin D has been shown to play an important role in immune system functioning, both by heightening the body’s responses to invading bacteria and preventing the immune system from attacking normal tissues.

3) Where do we get vitamin D?

There are two major sources: sunlight and diet. Sunlight is the more efficient way to get vitamin D.

The good stuff

4) What happens if we don’t get enough?

Historically, the connection between lack of sunshine and rickets–soft, deformed bones–was made in the 19th century. (Pelvic bones shrunken and deformed by rickets were the cause of many deaths in childbirth in those days.) Later, a lack of vitamin D was identified as the cause of rickets. Osteoporosis, especially in women, also results from inadequate vitamin D. Recently, as vitamin D’s immune system role has become clearer, a lack of vitamin D has also been linked to a number of serious chronic conditions, such as Type 1 diabetes, systemic lupus erythematosis, and multiple sclerosis.

5) Why is there so much vitamin D deficiency these days?

It’s mainly due to decreased sun exposure and poor diet.

6) So why are breastfed babies at risk for vitamin D deficiency?

Many pregnant or lactating women don’t have enough vitamin D for their own bodies, let alone enough to build up their babies’ supply. A mother’s problem soon becomes her baby’s problem, too.

More to come…

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Filed under Nutrition, Science