Vitamin D and Your Immune System

Every now and then, I get to interview an expert who is so passionate about his or her work that the enthusiasm is infectious. That was certainly the case with John S. Adams, a professor at David Geffen School of Medicine at UCLA and an expert in vitamin D’s role in the immune system, whom I spoke with last month for an upcoming article in AARP the Magazine. Since I wasn’t able to include in that article even a fraction of what we talked about, and it’s worth sharing, I decided to cover the rest here.

Note: Look for my “Immune-Boosting Foods” article in the October/November 2012 issue of AARP the Magazine for the rest of the interview, and for other information about how to feed your immune system during cold and flu season. I will add a link to the article as soon as it becomes available.

Vitamin D has to be metabolized to its active form in the body, called 1,25-dihydroxy vitamin D, and that is essentially a hormone and controls the genes inside human inflammatory cells (mainly the macrophage) that regulate immune function. When bacteria or pathogens enter your body it’s the job of the macrophage to go to the site of infection, ingest those microbes (take them inside the cell), and then generate antibiotics inside that cell to kill the ingested microbe. If you don’t get enough D, it cannot make enough of the hormone to support those genes that are necessary for killing microbes.

It’s the very early stages of infection where vitamin D seems to be most important in getting rid of infection, to kill the ingested bugs. [Research so far shows that] if you give vitamin D supplements to people after they’ve been infected, there’s really not much impact on the course of disease.

We don’t have any clinical data in human infectious diseases to tell us what the optimum level is to prevent infection, but it looks like there’s a linear correlation. So the more you feed a macrophage, the better it is at killing the ingested microbe. It’s a “more is better” kind of approach. For our experiments we try to get [subjects’ blood] levels above 30 nanograms per mil, which shows significant changes in the lab.

The idea is that if your D levels are low, you do have reduced immunity to some very common infectious agents. And the ones we particularly study are tuberculosis and AIDS. For tuberculosis, about 1/3 of world’s population (2.5 billion people) are infected with the bacteria that causes TB. In the US it’s lower, but it’s a major problem in developing world. Of those infected, 2 million die every year. The reason they die is they get re-infection disease. All these people are carrying these germs in their macrophages. They don’t die of the original infection—they die of secondary, or re-infection. So our hypothesis is that vitamin D is there to make sure that we kill those bugs when they first come into the macrophage, so we can prevent them from multiplying and re-infecting the host. The AIDS virus is like TB—it gets ingested by cells and lives very happily there. The same mechanisms would kill AIDS virus in an infected cell.

Sub-Saharan Africa and South Asia—the places in the world that are most affected by AIDS and TB. Most people who die of AIDS die of TB infections. They are also the most D-insufficient. The more pigmented you are, the less vitamin D you can make in your skin. So if that’s what you’re relying on but you’re not getting outside as much as you used to (you work indoors, etc.), you’re not allowing the normal human process for making D to occur effectively. In the US, for individuals who are highly pigmented, like African Americans, 97% of them have vitamin D levels less than 30 nanograms per ml (the Institute of Medicine suggests we need at least 20 nanograms per ml in our blood for bone health; the Endocrine Society thinks the cutoff should be 30 nanograms per ml). There are no studies that tell us what the optimal levels are inside a person.

People who have immune suppression—such as natural immune suppression from HIV, or who are taking drugs like steroids (prednisone) to suppress the immune response, or who are receiving chemotherapy that kills off inflammatory cells—need extra amounts of vitamin D.

In the US, dairy products* and cereals and breads are artificially fortified. The greatest natural source is the muscle and fat of wild-caught fishes: salmon is best, since they ingest phytoplankton, which is the richest source of vitamin D on the earth. If you buy farm-raised salmon, it has only about ¼ of the vitamin D in its flesh compared to wild-caught salmon because the fishes don’t have access to the phytoplankton. These are best sources of D3.

Certain mushrooms are also good sources of vitamin D2, but you’ll have to read the AARP article to learn more!

*[Note: Milk is regularly fortified with vitamin D, but products made from milk, such as yogurt and ice cream, are frequently not fortified. Check nutrition labels to be sure.]

We would like people to get enough naturally [through sun exposure and diet, as opposed to supplementing], but it’s not realistic for many people. So how much do you need, and how should you get it? The Institute of Medicine says to maintain your blood levels at 20 nanograms per ml, which requires two things: First, that you get your levels above that to begin with, and then that you maintain it. In the populations we work with, you have to give them loading doses to get them normal and then maintenance doses to keep them normal. We give them 500,000 IU orally over a short period to get them normal. To keep them normal we give them between 1,000 and 1,500 IU per day. Get screened by your doctor to see if you’re low; it’s a simple, inexpensive blood test and quite reliable in most instances.

You can also boost your levels by exposing your unprotected skin to the sun in short, 10–15 minute bursts on at least 20% of your body, but again, keep in mind that people with highly pigmented skin can’t produce vitamin D as efficiently this way, and people who live far away from the equator [like me in Boston!] are also at a disadvantage because the sun’s rays aren’t as strong.

There are no cause-and-effect data to demonstrate there’s a danger in getting too much vitamin D. Epidemiologic studies such as NHANES III show that if values are less than 30 nanograms per ml or greater than 70 nanograms per ml, there’s a significant increase in all-cause mortality. The bottom of that curve—the sweet spot—is somewhere between 30 and 40 nanograms per ml. The curve is much steeper on the lower end, and the deaths there are almost always due to cardiovascular disease. On the high end, that slope is much shallower, and the deaths are almost always caused by cancer (especially pancreatic cancer). But remember these are not cause-and-effect studies—they are only completely indirect evidence.