KATHLEEN M. THIESSEN is a senior scientist at SENES Oak Ridge, Inc., Center for Risk Analysis. From 2003 - 2006, Dr. Thiessen served as a panelist for the National Research Council's (NRC) review "Fluoride in Drinking Water: A Scientific Review of EPA's Standards." She has extensive experience evaluating exposures, doses, and risks to human health from environmental contaminants and in the use of uncertainty analysis for environmental and health risk assessment. More recently, Dr. Thiessen has led a working group on dose reconstruction for the International Atomic Energy Agency's Biosphere Modeling and Assessment Methods program. She received her Ph.D. in genetics from the University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences.

On July 29, 2006, Dr. Thiessen spoke with Michael Connett of the Fluoride Action Network, concerning her review of the toxicological literature on fluoride. Dr. Thiessen had earlier presented her findings on "Fluoride and the Endocrine System" to the 2nd Citizens' Conference on Fluoride. To access a copy of Dr. Thiessen's power point presentation at the conference, click here.

TRANSCRIPT of Interview with Dr. Kathleen Thiessen
July 29, 2006

MICHAEL CONNETT: So, Dr. Thiessen, you recently took part in this review from the National Research Council on fluoride toxicology?

THIESSEN: That's correct.

CONNETT: Three years, a lot of time, a lot of papers, a lot of review -- what are some of the issues or points that stick with you, that you feel are important about this issue of how fluoride affects human health? What should we know?

THIESSEN: I think it's important to know that our committee unanimously said that the existing regulatory limits for fluoride in drinking water are not protective. We did that on the basis of health effects that have long been associated with fluoride: dental effects and skeletal effects.

We also pointed out a number of areas where there are, or seem to be, adverse health effects that have not historically been associated with fluoride or at least not in the mainstream literature -- the government agency literature and such. And we said these need to be looked at, that some of these could be important for Americans even at the regular drinking water levels, even without approaching the limits.

CONNETT: And you particularly focused in on the endocrinology aspect of the issue. As you were saying, in the past, the effects of fluoride, the focus, has been on the teeth or bone. But there's not much discussion or awareness that fluoride might affect the endocrine system. What would you say about this issue about how fluoride might affect the endocrine system?

THIESSEN: There is a considerable body of literature that indicates that fluoride exposure does affect the endocrine system, or parts of the endocrine system, in at least some individuals. There's probably a number of reasons why some individuals show effects and others do not and these include dietary effects, genetic effects, level of individual exposure -- as opposed to population or group exposure.

The historical database, it's been there for a while, many of the studies were done before people were thinking about endocrine effects of any sort. Many of the older studies did not have the technological capabilities available to them that more recent studies have had so it's been interesting scientifically to piece together the available information.

CONNETT: Is there evidence to suggest that fluoride can affect thyroid function, and if so how?

THIESSEN: There is evidence. There are a number of studies that show increased parts of the population with goiter, overgrown thyroid, which is a natural attempt of the body to compensate for underfunctioning of the thyroid or insufficient iodine. There are several studies showing that there's an increase in the prevalence of goiter with an increase [of] fluoride concentration in the drinking water. There are other studies that show differences in the mean hormone measurements in people in these groups. There's not enough studies that show percent of affected individuals, percent of individuals with thyroid stimulating hormone (TSH) values that are above normal -- which would indicate hypothyroidism -- but they're certainly enough to say that there are effects.

CONNETT: Could you explain the basis of concern for why fluoride could be a contributing factor to hypothyroidism?

THIESSEN: Fluoride appears to have an anti-thyroid effect, or produce hypothyroid effects, in some individuals -- meaning that it causes the overall thyroid function to be less than it should. There are several possibilities for it.

It's important to note that these effects seem to be more severe in people who already have an iodine deficiency, or they occur at lower levels of fluoride exposure with an iodine deficiency.

There could be an actual direct effect on thyroid function -- the thyroid gland itself -- in terms of how much hormone is being secreted. Because of the complexity of the whole situation, there are other effects that are possible. One very likely one is an effect of fluoride to inhibit the enzymes that are called the deiodinases which convert the secreted form of thyroid hormone (T4) into the active form of thyroid hormone (T3). So the thyroid gland may be functioning perfectly normally but an enzyme in the peripheral tissues is being inhibited so that the active hormone is not being delivered to the tissues in the concentration it should be and so the individual is essentially hypothyroid.

CONNETT: Iodine deficiency --- does it occur in the United States?

THIESSEN: The CDC, Centers for Disease Control, has reported that approximately 12% of the US population -- or the sample of the US Population [tested] -- had urinary iodine levels below what's considered the adequate range indicating an inadequacy of dietary iodine intake. Part of the reason for that, supposedly, is that there's been a push in the past decade or two for people to reduce their salt consumption. And since, for many people, the major source of iodine in the diet is from table salt, if you reduce that you reduce the iodine intake.

CONNETT: And why is that of concern with this issue of fluoride?

THIESSEN: Iodine intake is of concern for proper thyroid function. The body has to have enough thyroid hormone to keep normal activities going, and in the developing fetus and the child it’s essential for normal growth and development to happen -- especially for neurological development. So it's an essential element. With respect to fluoride, if fluoride -- or if any other agent -- is causing a reduction in thyroid function, or is causing the active form of the hormone not to be made in the proper quantity, you've got a problem.

CONNETT: So fluoride could make an iodine deficiency worse? Maybe if you could summarize the issue of fluoride and iodine deficiency?

THIESSEN: The available information indicates that the effects of fluoride on thyroid function is worse if the person or animal has an inadequate dietary intake of iodine. Or, the effects may occur at lower fluoride exposure levels if there's inadequate iodine intake. So lack of iodine intake makes an individual more susceptible to the effects of fluoride exposure; fluoride exposure makes an iodine deficiency worse.

CONNETT: And when you looked at the doses that were associated with the effects on the thyroid in iodine deficient and non-iodine deficient individuals how did they compare with the doses that many Americans would receive?

THIESSEN: Many Americans are getting fluoride exposures in the ranges associated with thyroid effects, especially if there's an iodine deficiency. We're talking average levels of fluoride exposure of around 0.03 milligrams-per-kilogram per day for adults in the US. That's average. Many are above that, many are below that. And the levels of fluoride exposure at which one sees thyroid effects in some individuals -- not everybody -- with an iodine deficiency are right around that same range.

CONNETT: So there's an overlap there?

THIESSEN: There's an overlap there.

CONNETT: Now with water fluoridation, it's a policy where we sort of are treating everyone with the same general dose, or concentration, of fluoride. What would be your response to the notion that we can treat everyone in the population -- or assume that everyone in the population is going to respond the same -- to the same dose of fluoride?

THIESSEN: Doesn't matter what contaminant you're dealing with, to expect the same response for everybody is silly. It's not taking into account dietary variability, it’s not taking into account variability of water consumption, it’s not taking into account genetic susceptibility to possible effects of whatever contaminant you're dealing with.

CONNETT: And is there evidence to suggest that individuals respond differently to fluoride? Are some people more susceptible to fluoride?

THIESSEN: There is evidence, from a variety of sources, that individuals respond differently to fluoride exposure. It depends on what endpoint you're looking at, but certainly there are differences in nutritional aspects between individuals -- those who are getting adequate supplies of nutrition generally and certain elements in particular. There are also genetic variants within the population. Different genetic forms of an enzyme may respond differently. That's certainly there. There's also -- individuals vary widely in their exposure, because they have different sources of exposure. Their water intake varies so widely, that sort of thing. I would expect for just about anything to see a wide range of population response.

CONNETT: So do you have any concerns about water fluoridation and if so what would those concerns be?

THIESSEN: Speaking as a scientist, based on the information I have looked at, we're dealing with uncontrolled and unmonitored exposures to an agent that is known to have adverse effects on humans. I have no problem with it being in the list of drugs and people having it with a prescription, as with any others, if there's a doctor -- or appropriate medical professional -- monitoring the exposure and the side effects and whether its effective.

CONNETT: Speaking of susceptible populations to fluoride, what about people with kidney disease?

THIESSEN: Well, people with kidney disease are going to clear less fluoride from their body. They're going to retain more fluoride because the normal route of elimination of fluoride is through the urine, so if the kidneys are not functioning properly, they will retain more. So any effects that are due to an accumulation of fluoride in the bones, for instance, or to a higher level of fluoride in the bloodstream, they're at risk for that. Also, many kidney patients will drink more water than healthy people and so that means their fluoride intake is already higher than healthy people would have.

CONNETT: And what kind of adverse effects could kidney patients experience?

THIESSEN: There were papers in the 1970s describing skeletal fluorosis in kidney patients, partly because of the high consumption of water and partly, probably, because of the reduced clearance of fluoride.

CONNETT: And diabetics?

THIESSEN: Diabetics -- particularly those whose diabetes is uncontrolled or inadequately controlled, those who have not yet been diagnosed or who are not doing well on treatment -- they have a higher water consumption, can be considerably higher. Many people when they are first diagnosed with diabetes have thought they were healthy when in fact their thirst was extremely high. So, because of that high water intake, they're getting more fluoride. Down the road, many diabetic patients eventually develop some degree of kidney failure. So then you've got that problem again of reduced clearance of fluoride.

CONNETT: So could you list the various populations who will have increased susceptibility to fluoride?

THIESSEN: Well, it depends what effects of fluoride you're talking about. But, many effects of fluoride, the people who will be most susceptible to them are those who have dietary insufficiencies, either general or specific elements (calcium, iodine in particular). Those who have a high water consumption, they will have a much higher exposure than is generally considered. And for people who are athletes or who work outside or live in hot climates, drinking enough water is an important thing -- you don't want them to die of heat stroke. People who have kidney problems and who retain more fluoride, who don't clear it out, they are at higher risk for fluoride-related problems. Those would probably be the main groups. Younger people, children, babies who have a higher fluoride intake per unit body mass, especially infants on formula.

CONNETT: Speaking of which, what would you say about this issue of infants and fluoride exposure? Would you recommend that infants not receive fluoride in their formula?

THIESSEN: Infants should not receive in their formula, no.

CONNETT: And why is that?

THIESSEN: The exposure of fluoride per unit body weight in an infant is large. The fluid consumption is very high because that's how they get in all of their nutrition. It's a liter, two liters a day, depending on the age, size, of the infant. Many of the effects -- we don't know all of the effects because nobody has really looked at what are the effects of fluoride exposure in the very young. We know that some of [fluoride’s] effects will happen at various exposure levels. We know that some of those exposure levels will occur extremely easily in the very young. It's just not wise to do it.

CONNETT: So the exposure levels that infants are being exposed to, if they're drinking fluoridated water in the formula, how do they compare with the thyroid effects if they have an iodine deficiency?

THIESSEN: Oh, they're more than high enough if there's an iodine deficiency.

CONNETT: Is fluoride an essential nutrient?

THIESSEN: No, fluoride is not an essential nutrient. I’m not aware of any studies that have ever been able to demonstrate that. There have been a few that have tried. But there are very, very few sources that even now try to insist that fluoride is an essential nutrient. The general opinion by all concerned is that fluoride is not an essential nutrient. The body does not have a systemic requirement for it.

CONNETT: What's your thoughts on the push these days to target low-income communities for being who we want to fluoridate because they don't have as much access to dentists and dental care? What should people be aware of in that process?

THIESSEN: Well one of the reasons often given for providing water fluoridation is to even out the socioeconomic differences, to provide fluoride and the dental health benefits of it, to children who don't have access, or don't have as much access, to professional dental care. The York Report from England in 2000 said that they could not find any studies that demonstrated any leveling out of effects between socioeconomic groups based on fluoridation. The literature I’ve seen in the states -- and there've been very few studies -- show socioeconomic differences in dental health aspects, but they do not show effects with respect to fluoridation. I'm not aware of evidence that actually indicates that fluoridation will help even out the socioeconomic differences.

CONNETT: Is there reason for health concern because lower-income communities have higher diabetes rates, they have higher kidney disease, they have poorer nutrition?

THIESSEN: Right, the lower-income communities, there are many aspects for concern. One is lower access, or poorer access, to professional dental care [and] professional medical care. There are higher rates of a number of conditions. Some of these are probably due to nutritional deficiencies. They buy the cheapest food rather than the most nutritional food. They are probably more likely to have calcium deficiencies because they drink less in the way of dairy products. They drink more in the way of commercial beverages, for instance, that are made typically with fluoridated water. So the calcium intake is lower, the fluoride intake is higher. There is some evidence that suggests that the higher the fluoride intake the higher the calcium requirements which means their calcium deficit is even bigger.

CONNETT: So, is there reason to believe, evidence to suggest, that low-income communities could actually be more vulnerable to being harmed by drinking fluoridated water?

THIESSEN: I would expect low-income communities to be more vulnerable to at least some of the effects of drinking fluoridated water or fluoride exposure from whatever source.

CONNETT: And that's because?

THIESSEN: Because there are the nutritional deficits. The lack of access, or less access, to health care. Often a lack of education as to what corresponds to a good diet or healthy practices. A number of things.

CONNETT: In the NRC report, you've really kind of brought to light so many complexities on this issue. Some proponents of fluoridation say it has been proved to be absolutely safe. How would you describe the nature of the research showing that fluoridation is "safe" for everyone? What are the deficiencies in that literature?

THIESSEN: Well it's extremely dangerous in science to say there are no, no adverse health effects of fluoride, no something else. It's extremely difficult. All you have to have is one adverse health effect of fluoride to disprove 'there are no adverse health effects.'

CONNETT: One question I forgot to ask -- pineal gland and fluoride.

THIESSEN: The pineal gland. It's still not very well understood in terms of what its normal physiology is in the first place. But there are many things it is associated with: reproductive development, normal body rhythms, calcium metabolism, a bunch of other things. There is very little research available on fluoride effects on the pineal gland. What little there is suggests that it can disrupt melatonin production or disrupt the normal cycle of melatonin production. If that's real that could be part of the explanation for a number of fluoride effects. It could mean fluoride could have an effect on a number of different systems. It's one of those things that's really tough to get at. There's just not much information and it's a hard set of circumstances to try to study.

CONNETT: Fluoride's been found to accumulate in the pineal gland?

THIESSEN: Yes. There's one study from England in which the pineal gland from some number of cadavers were looked at in terms of what the fluoride concentrations were. The pineal gland is what's called a calcifying organ. It does get concretions, or calcifications, in it. Many other organs do this also and this has been known for the pineal for some time. And it's in those calcifications that the fluoride occurs. And most other, probably all other calcifying tissues, will also accumulate fluoride if there's fluoride exposure. The significance of this is just not known at this point.

CONNETT: The NRC review also found that fluoride might inhibit insulin secretion and impair glucose tolerance. Could you discuss this research, and its potential implications?

THIESSEN: There's a small but consistent body of literature suggesting that individuals with a high enough fluoride exposure -- or some fraction of individuals I should say -- will experience impaired glucose tolerance, higher blood sugar levels. The importance of that in this country is not known but certainly people do get fluoride exposures that reach the levels that have been associated with impaired glucose tolerance. There's one study that it's probably reversible, at least for young adults, when the fluoride intake is reduced. The impact of that is obviously potentially significant given the 6 or 8 percent that is thought to have type-2 diabetes. There are obviously a number of other factors that contribute: lifestyle issues and things of this sort, and probably genetic issues, at least for some individuals. But given the magnitude of the diabetes situation in the US, the possibility of fluoride exposure contributing to that needs to be looked at considering that two-thirds of the population has a substantial fluoride intake.

CONNETT: So what should communities faced with water fluoridation proposals consider, or know, about the NRC report?

THIESSEN: Well it's important to remember, again, that the NRC report did not specifically address fluoridation. We did not address the benefits, or supposed benefits. We did not address risks, or supposed risks of water fluoridation. We mostly looked at whether the existing regulatory levels of 2 and 4 milligrams per liter are protective. We said they are not. If 2 and 4 are not protective, is 1 going to be protective? Is there an adequate margin of safety between less-than-2 and 1? And clearly some of us who have been in the risk assessment business a while would think that there's probably not very much margin of safety there.

CONNETT: I'm glad you brought that up. You have been doing risk assessments for many different years on many different chemicals. When you look at the margin of safety that you usually expect with other chemicals and then you look at fluoride, what do you see?

THIESSEN: The concentration of fluoride that's used for supposedly the benefits is also in the range where adverse health effects are seen or begin to be seen. There's an overlap of the so-called beneficial range and the so-called adverse health effect range. And that's no margin of safety.

That's the sort of thing that indicates it would need to be dealt with on an individual basis to provide any benefits to an individual without putting that individual at risk. That would be roughly what's done with most other drugs.

CONNETT: And what is this notion of ‘margin of safety’ and why do we want a margin of safety?

THIESSEN: A margin of safety should be pretty much what it implies. That in order to account for things we don't know about, or an individual who sometimes drinks, or regularly has a higher intake than we think he does, or has exposure from other sources, or is more susceptible than the individuals we are used to dealing with. We have to allow for these variabilities and that's what the margin of safety is supposed to do.

Depending on the information base that's available, sometimes there's an extra margin of safety put in when we have information from animal studies and we don't have comparable information, or not enough information, from human studies. It's an extension of the principle of "first do no harm," of don't do anything that's going to be damaging. If we make a mistake, let it be on the side of safety.

CONNETT: On that point, when you think of water fluoridation and the word ‘precaution’, what do you see there? Is fluoridation a reckless policy?

THIESSEN: That would be one word to use. It's certainly unwise to provide unmonitored or uncontrolled exposures to individuals, large numbers of individuals, of any contaminant, or any potential agent, that could cause adverse health effects.

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