A new report from the National Academy of Sciences' Institute of Medicine says there is little evidence that vitamin D can do anything more than improve bone health — and that big doses might even do harm. NPR science correspondent Richard Knox explains how it should be used.
TONY COX, host: Vitamin D, over the past few years, has been billed by some as the health panacea in your medicine cabinet. Proponents of the supplement have recommended super doses of vitamin D to prevent everything from cancer to heart disease, diabetes, even autism, and the list goes on. But a new report from the Institute of Medicine at the National Academy of Sciences says there's little evidence that vitamin D can do anything more than improve bone health and that big doses of D may even be harmful.</s>TONY COX, host: If you have questions about vitamin D and the new report, give us a call. Our phone number here in Washington is 1-800-989-8255. The email address: talk@npr.org. And to join the conversation at our website, just go to npr.org and click on TALK OF THE NATION.</s>TONY COX, host: NPR health and science correspondent Richard Knox is with us to help sort out what we know and don't know about vitamin D, the so-called sunshine vitamin. And he joins us today from his office in Boston. Richard, hello, nice to talk to you.</s>RICHARD KNOX: Hi. Nice to be with you.</s>TONY COX, host: Let's begin with this. Let's explain what vitamin D is. Where do we get it and what does it do?</s>RICHARD KNOX: It's unique among vitamins, it's - because it's made in our skin, in our kidneys and livers from exposure to the sun. It's not easy to get from the diet. You can get it through fatty fish, sort of dark-fleshed fatty fish contain vitamin D and, you know, things like sardines as well. But you don't get it from any other places in the diet. That's why they fortify milk and orange juice with it.</s>RICHARD KNOX: It's necessary for bone health. We know that for sure. Long ago, people, kids especially, used to get scurvy. They would - I'm sorry, rickets. They would - their bones wouldn't develop normally if they didn't have enough vitamin D. It works with calcium in the diet. Vitamin D increases the body's ability to use calcium. So you need both nutrients in order to have healthy bones.</s>TONY COX, host: We have heard so much, Richard, about the health benefits of vitamin D in the past few years for all sorts of ailments, as we indicated at the top of the story. But this new report says, wait, wait, wait, not so fast.</s>RICHARD KNOX: That's right, yeah. It's been two years in the making. It was ordered up by the governments of United States and Canada. It's part of a process that goes on periodically to look at nutrients. The National -the Institute of Medicine, which is part of the National Academy of Sciences, has a group called the Food and Nutrition Board. And this group of 14 experts went over like nearly 1,000 studies and they, you know, had lots of hearings. They had commissioned a couple of government studies.</s>RICHARD KNOX: And they came up, finally, with this new set of guidelines that tells people what they think they ought to be taking in their diet and sometimes in supplements. But most people, it turns out, don't need supplements like the group says.</s>TONY COX, host: Now, the report still recommends, doesn't it, a daily intake of vitamin D that is higher than what had previously been recommended?</s>RICHARD KNOX: That's right. It's higher. It's not a whole lot higher. But in the past, it was, like, 400 for most adults and 600 for others. Now they're saying kids need 400 units a day, 600 units is enough for most adults. For those over 70, 800 units a day is a good idea.</s>TONY COX, host: Now, one...</s>RICHARD KNOX: And that should satisfy - excuse me. That should satisfy the needs of 98 percent of the population.</s>TONY COX, host: One other thing that's a little confusing to me personally, and maybe to some of our listeners, is - and I asked the pharmacist at my local grocery store - I didn't understand the difference between IU and - international unit and milligrams. And he - and I tried to get a comparison of one to the other, and he was not able to provide that. Is that an issue for us in terms of understanding just how much we are actually getting if it's 1,000 IU as opposed to a thousand mgs.?</s>RICHARD KNOX: Well, no. It shouldn't be confusing. I know it seems like it on the surface, but some nutrients are measured in the units of milligrams. Vitamin D is not. It's kind of a different standard, but you never see vitamin D doses measured in milligrams, so you can sort of forget milligrams when it comes to vitamin D doses. Calcium, on the other hand, is measured in milligrams.</s>TONY COX, host: All right. Now, one of the things that might also be helpful to our listeners, as we try to figure out what this - how to get to the exact number of IUs for vitamin D in terms of eating an equivalent amount of food, a fruit or vegetable, whatever the case may be, how do you get to 400 units? What do you - what could you eat that would be the equivalent of that?</s>RICHARD KNOX: Well, I'm told that the average, you know, decent diet will give you about 200 to 400 international units of vitamin D a day, so most diets will get you a good part of the way there. Exposure to sun is a pretty good way of getting vitamin D, and obviously that varies a lot from person to person or from time of the year - I mean, one season to the other. You know, some people wear more clothes. Some people put on more sunscreen.</s>RICHARD KNOX: For purposes of this report though, the Institute of Medicine experts decided to ignore sun exposure and just pretend that people, you know, got minimal sun exposure and look at all the other sources. And they told me they were surprised, actually, to find that most Americans do have adequate vitamin D levels even without supplements. So we don't really - most people don't need them.</s>TONY COX, host: Well, you know, that raises another interesting point about, for some people, the confusion surrounding this because we have this report which suggests that the levels of vitamin D that we intake should be something different than what we had perhaps been told before.</s>TONY COX, host: At the same time, many doctors have been - many people have been told by their doctors that they have a vitamin D deficiency. There seems to be some disagreement there. Are we hearing that correctly? Is there a disagreement? And if so, why?</s>RICHARD KNOX: Oh, absolutely. Yeah. That is a source of the, you know, main source of confusion, and I think it's totally understandable. People have been hearing, especially in recent years, that they need to get their vitamin D levels tested. Many doctors are doing it routinely and many people are being told you're deficient.</s>RICHARD KNOX: That's not a happy thing to hear. And you know, I think we need to spend a little bit of time on this because it really comes down to the question of what does deficient mean. And surprisingly, there is no agreed upon expert consensus on what inadequate or sufficient diet, you know, deficient or sufficient vitamin D level is.</s>RICHARD KNOX: You'd think there would be. There is for other nutrients, but not for vitamin D. And that's one of the things the panel says we really have to work on. So people have different definitions. Some of the proponents of large doses say that we probably should have a level of 30. That's 30 nanograms per milliliter of blood. And this group, the Institute of Medicine group, says no, 20 is sufficient and most people are well within 20.</s>RICHARD KNOX: It makes a big difference. If you use 30 as the level of - that everybody ought to be, then most Americans, maybe 80 percent or something, are deficient in vitamin D, and that's what many of the proponents of large doses and supplements say, that we have an epidemic of vitamin D deficiency. This panel looked at the evidence and says no, we don't.</s>TONY COX, host: All right. You know what, this is a good point for us to take some calls and have people, you know, chime in on this. Let's begin with Jeff in Vancouver, Washington. Hello, Jeff. You're on TALK OF THE NATION.</s>JEFF (Caller): Thank you very much.</s>TONY COX, host: Do you have a question or a comment?</s>JEFF (Caller): Yes. We have a one-year-old baby and we are giving her a regimen of 400 milliliters of - I'm sorry - milligrams of vitamin D supplement in the oil. And we've been to both medical doctors and naturopathic doctors and they recommend, because we're in the Pacific Northwest, low sun exposure that probably everyone is deficient. Does that sound right?</s>TONY COX, host: Thank you very for that, Jeff. What about that?</s>RICHARD KNOX: It sounds almost right. It probably is 400 units rather than 400 milligrams, as we were talking about earlier. The Institute of Medicine panel, which is making recommendations for both Canada and the United States, is saying that children under four should get 400 units a day and so, you know, you're probably well-advised to make sure your infant has that. Breastfeeding is not a good source of vitamin D. So that's another reason why young children need to have other sources.</s>TONY COX, host: Here's another call. This is Aimee(ph) in Patterson, California. Hello, Aimee. Welcome to TALK OF THE NATION.</s>AIMEE (Caller): Hi. I think it's really great that you're doing this right now, because I was just diagnosed with a vitamin D deficiency. My blood test actually showed I had 16 out of 30. I'm not sure why. But I would like to know if there are other alternatives to getting vitamin D besides, like, the milk and the juice, because I'm diabetic, and I'm also lactose intolerant. And, of course, you know, it's sometimes sunny in Northern California. But I was curious to know if there are alternatives, because I don't like pills.</s>TONY COX, host: That's an interesting question, Aimee. Thank you very much for that. So what would you say to her?</s>RICHARD KNOX: Well, first of all, I'm not a doctor. But it sounds as though the very best way is to get out in the sun on a fairly regular basis. So like 15 minutes of sun exposure through - for, you know, normal kind of clothing, exposing your arms and face and so on, I think would probably help.</s>RICHARD KNOX: Sixteen is below what the Institute of Medicine says they'd like to see people. It's not radically below, I guess. But you might consult your doctor and say, should I be taking a modest supplement of vitamin D? It's cheap. You can get it at the drugstore. But just don't - according to the Institute of Medicine panel, you don't have to take, you know, 1,000 milligram - 1,000 units, 2,000 units, 4,000 units.</s>TONY COX, host: Lisa(ph) from Placerville, California is standing by. I'm going to go to her in a second, because she has a question that is the same question that I had for you. But it's a little bit a different. I wanted to talk about any potential harm from taking vitamin D. And Alyssa wants to take that question just a little bit farther. Hello, Alyssa. Welcome to TALK OF THE NATION.</s>LISA (Caller): Hi. Thanks for taking my call.</s>TONY COX, host: Sure.</s>ALYSSA: My husband grew up in New Jersey. And when he was a young child, under four, he actually had an overdosed of vitamin D from sun exposure and ended up in the hospital. And so my question is, these people that are taking, you know, megadoses of vitamin D supplements, are they - you know, why aren't we hearing more of those effects? And is that, you know, possible? Is that kind of thing - I mean, about the overdose risk.</s>TONY COX, host: Thank you very much, Lisa. That was going to be my question. Not overdose per se, but whether or not there was harm from taking too much.</s>RICHARD KNOX: Yeah. There are several issues here. Let's see if we can kind of tease them out. First of all, I think overdosing on vitamin D from sun exposure is pretty unusual. This report doesn't address it. I think it's probably, for most people, not to worry about. The report does raise a concern about harms from high doses. It says that a maximum of about 4,000 units a day is what people should stay within. And that's really not because there's proven harm for higher doses. And certainly the proponents of higher doses say it's a really very safe thing, until you get to really, really, really high levels.</s>RICHARD KNOX: But the Institute of Medicine folks say that we just don't really know. There just haven't been a whole lot of studies. And there are sort of hints and some signals in the literature to suggest that there may be an increased risk of certain kinds of cancers such as pancreatic or esophageal. Not proven. There may be a reason to worry about heart disease from deposition of excess calcium in the arteries. Again, not proven.</s>RICHARD KNOX: One thing that is known about risk and harm is that kidney stones can result from too much calcium in the body. And remember, vitamin D increases the absorption of calcium. And one of the panel members was telling me this week that it used to be that kidney stones were rarely seen in women. It was more of a men's problem. And - but in recent years people are reporting more kidney stones in women. So people need to be a bit careful about doses, especially over 4,000 a day.</s>TONY COX, host: We're taking your questions and talking about the new recommendations for vitamin D. You're listening to TALK OF THE NATION from NPR News.</s>TONY COX, host: That last comment that you made about calcium actually is a perfect segue, Richard, for the question that I have for you next, which is we should note that the report that we are referencing also looked at calcium intake. Talk about the findings of the report in that regard.</s>RICHARD KNOX: Yeah. You're not hearing as much about that because it's not so controversial. They don't change very much from what had been thought before. There is a table that they - that's in the report that indicates that, you know, children under six months should get 1,000 - excuse me, should get 200 milligrams of calcium a day.</s>RICHARD KNOX: As children age, and especially get into the rapid growth years, their calcium needs grow. So it's like 1,000 milligrams between the ages of four and eight, 1,300 in nine to 18, the adolescent rapid growth years. Then it goes back to 1,000, then older people need 1,200. That's probably more than you can absorb. But basically it's not a whole lot different from what had been thought before and not particularly controversial.</s>TONY COX, host: We had a question about fibromyalgia. I'm not sure if that's something that you feel comfortable talking about. I know I'm asking you on the air, which I probably shouldn't do. But if you feel like you can deal with that, we can take that caller. What do you say, Richard?</s>RICHARD KNOX: Well, I can talk in general terms about what the report says. It doesn't specifically address fibromyalgia, as far as I can tell...</s>TONY COX, host: I'll tell you what. Let me see if I can squeeze this person in really quickly. Katie(ph), I've got about 20 seconds for you to make your point.</s>KATIE (Caller): Hi. Thank you for taking my call. I have fibromyalgia and I've seen a lot of articles speaking lately about the power of vitamin D to reduce symptoms. So I am wondering if the report addressed fibromyalgia specifically and what it said and if it also addressed broader, other health issues like cancer and things that have also been identified as vitamin D?</s>TONY COX, host: Thank you very much. We're gonna try to see if we can get that answer for you. What do you say? As our time - we've got about a minute or so left.</s>RICHARD KNOX: Sure. Well, the short answer is that the panel does not find health effects from vitamin D doses of any sort, any level, beyond bone health. That's really undisputed. But for all sorts of other things that are claimed, it just didn't find the evidence was very strong. That may change as we get more evidence and there are studies. But you know, the study that exist so far are not considered, you know, strong enough to make a recommendation that people take doses for that reason.</s>TONY COX, host: Would you consider this a breakthrough report?</s>RICHARD KNOX: No. I think it's not a breakthrough. It's kind of a consolidation of a whole lot of evidence that's piled up over the past 10, 13 years since the last recommendations. And you know, I think it's striking to a lot of people because people have been hearing that vitamin D was really important for a lot of things. And this group says not proven.</s>TONY COX, host: We appreciate the time that you gave us, Richard. Thank you very much. NPR health and science correspondent Richard Knox, joining us today from his home in - his home office, that is, in Boston. Again, Richard, thank you.</s>RICHARD KNOX: Sure, any time.