Wednesday, March 10, 2010

A Mechanism for the Effects of Vitamin D on Immune Function

Our pediatrician is a big proponent of vitamin D supplementation, and thanks to her, everyone in the family regularly takes vitamin D. She referred us to the GrassrootsHealth.org website for more info about her recommendations. I did some PubMed searching, too, and decided that I agreed that the available evidence suggested that vitamin D supplementation might be a good idea- or at least that it wouldn't be a bad idea. We all know that vitamin D is essential for strong bones (this is because we can't absorb calcium without it), but one of the other things that vitamin D is supposed to help is your immune function.

I submit that "improves immune function" will be irresistable to just about any parent with a child in day care. And indeed, after we started giving Pumpkin vitamin D, I noticed a drop in the number of illnesses in our family (most of our illnesses come home from day care, and Pumpkin is the first one to get sick). However, she had also been at day care for awhile, and presumably built up some immunity to various things, so I considered this suggestive, but nothing more.

This week, I cam across a recent article in Nature Immunology by von Essen, et al, which adds support to the idea that vitamin D is essential for proper immune function. (You can read the abstract of the original paper without a subscription. Here is a write up of the paper, too.)

The paper looksat the function of one type of immune cells, called T cells. T cells are far more responsive to antigen after they have been "primed"- i.e., exposed to antigen once. The current model to explain this involves the fact that T cell activation can occur via two different signaling pathways. The first pathway dominates in "naive" T cells (T cells that have never been exposed to antigen), while the second dominates in T cells that have previously been exposed to antigen. The second pathway is far more efficient than the first, which explains why primed T cells are more responsive than naive ones.

But how do the primed T cells switch to the second pathway? That is where the new paper comes in. The researchers show that the expression of one key protein in the second pathway, phospholipase C gamma1, is increased by the combination of vitamin D and its receptor (cleverly called "vitamin D receptor", or VDR). The expression of VDR, in turn, is increased by the activity of the first pathway. So, the T cells turn on the second, more active pathway using the same pathway that they use to respond to antigen the first time they "see" it- but only if there is sufficient vitamin D around. The researchers even showed that T cells isolated from people with low serum levels of vitamin D were less responsive to antigen than T cells from controls with normal levels of vitamin D.

Maybe it is because my background is in biochemistry and biophysics, but this is the sort of study I like to see when I'm trying to evaluate the benefits of a supplement. Correlative population studies are all well and good, but I'm always a little suspicious of them. Human beings aren't lab animals- it is very hard to control for all of the confounding variables in how we live our lives. A population study indicating a correlation between levels of some vitamin and a certain outcome is a nice story, but it is only the outline of the story. A biochemical mechanism adds some satisfying detail to the story.

And here is the ironic twist to this story- as I write this, my nose is blocked with the second or third consecutive cold I've had this season, which just goes to show that no supplement can guarantee you perfect health.

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I am not a medical doctor. This post should not be construed as medical advice. I read the entire paper, but as an interested scientist, not as a careful reviewer. If you're wondering about whether or not you or your children should take vitamin D supplements, all I can really tell you is to talk to your doctor and/or do your own research.

9 comments:

  1. Very interesting. Thanks for sharing. I like a scientific explanation/theory for how and why also.

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  2. Cloud, what kind/brand of supplement do you use for Pumpkin? Are you relying on your breastmilk to supply Petunia's needs until she can take a supplement of her own?

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  3. The lab next to ours studies asthma and COPD, and they've found that vitamin D seems to help control asthma. Neat stuff.

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  4. @Bitts- both kids get Carlson vitamin D drops. You just have to give one tiny drop. Petunia gets the baby formulation every day (this is in line with recent AAP recommendations). When she's going to day care, I put it in her first bottle. On the weekends, I put it on my nipple before her first nursing.

    Pumpkin gets the 1000 IU formulation 3x/week.

    I take capsules of whatever brand they had at the store.

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  5. @Cloud, FYI, my Google account is Bitts (it signed me in automatically) but you know me as MrsHaley. Hi!

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  6. That's the kind of science I like too! Show me how the supplements actually make a difference in the biochemistry, not just some correlative study!

    Thanks for writing all this up. We are about to start the Pumpkin on daily vitamins, so it's nice to know how it might help her stay healthy. And now I'm actually considering the vitamin D drops for the Pookie...

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  7. You're preaching to the choir on the benefits of Vitamin D. Love it! I'm also just as militant about the benefits of Omega 3's.

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  8. Hi there - I am visiting after seeing your recent comment on Mom-101 and I saw this post. There has been a lot written recently regarding the research into the effects of Vitamin D and the new belief that it supports a healthy immune system much more than Vitamin C which was always previously regarded as a good option. My daughter is 3 and still will not drink milk - she was BF and then switched to water only when I weaned her. When she started preschool last fall she was taking Gummy Vites Vitamin D supplements and did not get sick at all. Then a couple of months ago she decided she no longer liked them and I tried in vain to find a substitute - during which time she got sick three times. My nephew had scarlet fever as a baby and had to take lots of antibiotics. Since then (he is now four) he has been continually sick, catching everything going, until my sister-in-law started him on Vitamin D supplements last fall and since then he has only been sick once and recovered much more quickly than usual when he did become ill.

    So I for one believe this research. The Gummy Vites are great if your child will take them. I now have my daughter on Target's own brand infant and toddler multivitamin drops - she won't drink her water with the drops added but will take a little medicine cup with the dosage and a little bit of water added. We refer to it as her medicine.

    Just in case that helps anyone else trying to solve the Vitamin D issue of a non-milk drinking toddler!

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  9. Hi, Aging Mommy! Welcome!

    We've had mixed luck with getting Pumpkin to take her supplements, too (we also try to do fish oil, since she doesn't really eat fish).

    Right now, we're using the Carlson brand of drops, and we only have to get her to take a single drop to get the vitamin D into her. I suspect she'd like the Gummi Vites, since she loves gummy worms. I may try those if she ever starts refusing her drops. Thanks!

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