Research on mercury is highly variable.  Very few studies document any serious health effects unless the exposure is very high, something that is very rare.  Some studies even find favorable effects from mild exposure while other report harm.  Clearly, huge numbers of studies show that people who eat more fish are healthier in numerous ways including less dementia in old age.

Methyl Mercury in Fish no Harm to Kids in Best Study: A study of 711 mother-child pairs in the Seychelles where 85% of population eats fish daily found no evidence of harm to children through 5 ½ years of age. JAMA 8/26/98. Exhaustive update study of 643 children from before birth to 9 years of age shows no detectable risk from the low levels of mercury their mothers were exposed to from eating ocean seafood, Lancet 5/16/03. Children born to mothers-to-be who ate an average of 12 meals of fish a week – about 10 times the average U.S. citizen eats – showed no harmful symptoms. U Rochester Medical. The children have been evaluated five times since their birth. Fish with similar levels of mercury and women had 6 times US average according to hair samples.

Methyl Mercury Reported to Harm Children: In a study of Faroe Island children by Harvard, cord blood samples at birth and hair samples were taken at ages 7 and 14. Some 1,022 mothers and their children from the Faroe Islands participated in the research. The mothers’ hair mercury levels at childbirth in most cases exceeded 1 microgram per gram, the exposure limit recommended by the National Research Council and the (EPA). At follow-up, children showed much lower levels. The latency of the electrical transmission from the acoustic nerve to the pons was significantly increased at higher intrauterine exposure to mercury. This observation was found to be true both at 7 years and at 14 years. At higher mercury exposures, the children were less capable of maintaining the normal variability of the heart rate. J Pediatrics 2/04

No Relationship Mercury and Heart Disease in Large Study: 33,737 health professional in Harvard study had toenail clipping obtained and 5.5 year follow-up. There was no relationship between fish intake, mercury levels and heart disease even in dentists who did have higher levels. Mercury and the risk of coronary heart disease in men. Yoshizawa K, Rimm EB, Morris JS, Spate VL, Hsieh CC, Spiegelman D, Stampfer MJ, Willett WC. N Engl J Med 2002 Nov 28;347(22):1755-60

No Effect Found in Small Newborn Study: Exposure to fish-Hg during pregnancy and lactation were studied in 100 women and newborns from Porto Velho at birth and at 6 months in exclusively breastfed infants. Women consuming <2 fish meals/week showed less median hair-Hg (3.5mugg(-1)) than women that consumed 2 fish meals/week (5.7mugg). Median total Hg in maternal hair (5.4mugg(-1)) was higher than in newborns (1.6mugg(-1)). The infants with multiple delays were born from mothers with range of hair-Hg comparable to mothers of normally developed infants. Maternal mercury exposure and neuro-motor development in breastfed infants from Porto Velho (Amazon), Brazil. Marques RG, et al. Fundacao Universidade Federal de Rondonia, Porto Velho, RO, Brazil. Int J Hyg Envir Health 2006 Sep 28. Also, no difference in hair mercury was found in time to pregnancy in 193 Japanese women study. Int J Hyg Envir Health 2006 Jul;209(4):337-44.

Mercury in Fish Harmful During Pregnancy, Not After: A cohort of 1022 consecutive singleton births in the Faroe Islands, where increased methylmercury exposure occurs from traditional seafood diets that include pilot whale meat. The prenatal exposure level was determined from mercury analyses of cord blood, cord tissue, and maternal hair. At age 14 years, 878 of 1010 living cohort members underwent detailed neurobehavioral examination. Prenatal methylmercury exposure was significantly associated with deficits in finger tapping speed, reaction time on a continued performance task, and cued naming. Postnatal methylmercury exposure had no discernible effect. A doubling on mercury levels lowered performance by 5-10%. Pilot whole meat was unusually high in mercury. Impact of prenatal methylmercury exposure on neurobehavioral function at age 14 years. Debes F, et al. Faroe Islands, Denmark. Neurotox Teracol 2006 May-Jun;28(3):363-75.

Mercury in Fish Harms Fertility: The average person in Hong Kong consumes fish or shellfish four or more times a week averaging about 132 pounds of fish per year. Even though the mean mercury level in store-bought Hong Kong fish was only 0.12 mg/kg, corroborating evidence is presented from numerous studies to support the view that mercury bioaccumulates. By the time a typical Hong Kong male reaches 30 years of age he will have accumulated approximately 4 mg/kg mercury in his hair. By age 60, his hair mercury levels will have increased to about 7.5 mg/kg. Hair is a useful indicator of mercury exposure. In the U.S. over a million hair samples have been examined for mercury (mean, 1.5 mg/kg). The mean hair mercury concentration for over 200 Hong Kong residents was 3.3 mg/kg which is more than double the U.S. mean. Two lines of evidence support the hypothesis that fish is the major source of methyl mercury in the diet of Hong Kong residents. 1. Individuals consuming 4 or more meals of fish per week had a hair mercury of 4.07 mg/kg dry weight of hair while those consuming fish less frequently had significantly lower levels (2.56 mg/kg). 2. Hong Kong residents that consume no fish had only 0.38 mg/kg hair mercury. The World Health Organization has adopted the U.S. EPA levels for mercury and recommends that food with mercury concentrations of 0.5 mg/kg or more should not be sold for human consumption. Data presented in this paper are consistent with the notion that adoption of a 0.3 mg/kg mercury guideline would benefit residents in countries where rates of fish consumption are significantly higher than in the U.S. Japan, for example, has already adopted a 0.3 mg/kg mercury guideline. In Hong Kong there is a significant correlation (p < 0.05) between male subfertility and the level of mercury in the hair of males between the ages of 25 and 75. Our study of individuals who have been eating mercury contaminated fish steadily for many years suggests that a daily mercury intake of only 0.3 to 0.7 mg/kg body weight may be sufficient to inhibit spermatogenesis in some Hong Kong males. Male subfertility has been correlated with both elevated mercury and the presence of various organochlorines in the diet. To determine whether fish sold in Hong Kong with elevated levels of mercury also had elevated levels of organochlorines we analyzed fish for both mercury and organochlorine content of their dorsal muscle tissue. Because analysis of fish tissue for lipids and a wide range of organochlorines is both very time consuming and expensive, only 15 different species of fish were tested. Organochlorine concentrations were low and there was no correlation between mercury and organochlorine in the 15 fish tested for both organochlorines and mercury. As a result of these tests we concluded that mercury could not be ruled out as the principal causal factor associated with the lack of fertility in Hong Kong males. Chemosphere 8/98:991

Says Risk Not Clear: Lack of demonstrated neurotoxicity among fish-eating populations has been cited by the World Health Organization and others as supporting an adult LOEL (lowest observed effect level) of > or = 200 ppb blood mercury equivalent. Researchers reviewed 13 published evaluations of neurologic status as related to tissue mercury or methylmercury concentration in long-term fish-eating populations. Review criteria included study size, design (sampling strategy, characterization of exposure, characterization of outcome) and data analysis. No case of classic Minimata disease is described in the 13 studies. Also, no study clearly shows a threshold tissue level above which any form of neurologic dysfunction occurs. A study by Valciukas et al. shows no evidence of neurologic impairment in groups with blood mercury of 10-20 ppb. Studies by Spitzer et al. and McKeown-Eyssen and Reudy suggest correlation of neurologic dysfunction with rising blood mercury concentrations in the 60-120 ppb range. While other studies show no effects associated with rising mercury dose, numbers are small, participant self-selection likely and the clinical assessment limited. Together the 13 studies describe neurologic examinations in approximately 50 fish eaters having a blood mercury equivalent above 200 ppb; of these subjects, neurologic dysfunction consistent with methylmercury exposure was found in as few as six and as many as 15. We conclude that the oft-cited LOEL for (methyl)mercury of 200 ppb in blood is not supported by these studies. Neurotoxicology 1996 Spring;17(1):177-86

Hormetic Effect Said More Common with Mercury: Calabrese claims that mercury is perhaps the most studied element showing a hormetic effect. Discover 12/02 p. 80. CDC follow-up of 100,000 infants given vaccines with mercury ended up having fewer motor tics, delayed speech and other pathologies.

Dentist More Memory and Kidney Problems: This study of 180 dentists by researchers at the Glasgow Royal Infirmary in Scotland found they had up to four times the normal level of mercury in their urine and nails and had more kidney disorders and memory lapses than the general public. Those with higher levels, more problems. 4/27/02 Reuters(London). Ed: This is a very small study with no follow-up when compared to the much better 33,000 person Harvard study above.

Amalgam Fillings Very Weakly Linked to MS: In a study of 20,000 new New Zealand soldiers, there was a non-significant link between the number of amalgam fillings and multiple sclerosis (adjusted hazard ratio (HR) of 1.24 (P = 0.06), but there was no association with chronic fatigue syndrome (HR = 0.98), or kidney diseases. Further follow-up of the cohort will permit investigation of diseases more common in the elderly. Health effects of dental amalgam exposure: a retrospective cohort study. Bates MN, Fawcett J, et al. Porirua, New Zealand. Int J Epidemiol. 2004 Aug;33(4):894-902.

Amalgam Fillings Not Linked to MS: In a case-control study of 132 MS patients and 423 controls, researchers found only a trend toward a higher number of dental fillings in cases than controls. The odds ratios for exposures of different duration and with different numbers of amalgam fillings were not statistically significant. Multiple sclerosis and dental amalgam: case-control study in Ferrara, Italy. Casetta I, Invernizzi M, et al. University of Ferrara, Italy. Neuroepidemiology. 2001 May;20(2):134-7

Bad Teeth, Not Amalgam Fillings Linked to MS: In a case-control study of 39 female MS victims and 62 controls, the odds of being a MS case increased by 9% for every additional unit of DMFT index of dental caries. This represents a 21% increase in risk of MS in relation to dental caries in this population. There was no difference between cases and controls in the number of amalgam fillings or in body mercury or lead levels. There was a significant correlation between body mercury levels and the number of teeth filled with amalgam Multiple sclerosis, dental caries and fillings: a case-control study. McGrother CW, Dugmore C, et al. University of Leicester. Br Dent J. 1999 Sep 11;187(5):261-4

Amalgam Non-Significant Link to MS Probably Just Bad Teeth: In a case-control study of 143 MS patients and 128 controls, neither the number nor the duration of exposure to amalgams supported an increased risk of MS. After adjustment for age, sex, smoking, and education those who had more than 15 fillings had an odds ratio (OR) of 2.57 compared to those who had none; for individuals whose first amalgam was inserted more than 15 years prior to the study, we found an OR of 1.34. Although a suggestive elevated risk was found for those individuals with a large number of dental amalgams, and for a long period of time, the difference between cases and controls was not statistically significant. Dental amalgam and multiple sclerosis: a case-control study in Montreal, Canada. Bangsi D, Ghadirian P, et al Hotel-Dieu Pavilion, CHUM, Montreal, Quebec, Canada. Int J Epidemiol. 1998 Aug;27(4):667-71

Campaign Against Amalgam Fillings: Opponents of mercury fillings compared 47 multiple sclerosis patients with silver/mercury tooth fillings (amalgams) to that of 50 patients with their fillings removed. Those with amalgams suffered significantly more depression on a BDI while their scores on the State-Trait Anger Expression Inventory indicated more anger. On the SCL-90 Revised, subjects with amalgam fillings had more depression, hostility, psychotism, and were more obsessive-compulsive. A comparison of mental health of multiple sclerosis patients with silver/mercury dental fillings and those with fillings removed. Siblerud RL. Rocky Mountain Research Institute, Inc., Colorado. Psychol Rep. 1992 Jun;70(3 Pt 2):1139-51. Ed: People worrying about their fillings for years might be expected to feel relieved after spending money to have them removed.  Advocates make biased researchers.

Dental Cavities Strongly Linked to MS; Maybe a Vitamin D Deficiency Effect: Comparing the geographical distribution of MS to those of dental caries found that the rates of death due to MS in Australian states are linearly related to the numbers of decayed, missing, and filled (DMF) teeth found in individuals from those states (P < 0.002). In the U.S., a strong positive correlation (P < 0.001) also exists. The prevalence of MS in 45 countries or areas correlates well with the frequencies of DMF teeth among children of school age in those locations (P < 0.001). The prevalence of MS also correlates well with the percentage of people with no teeth in certain countries (P < 0.001). The risk for dental caries is lower among the following groups: the lower socioeconomic classes in the United States of America; Chinese immigrants to England compared with natives; blacks compared with whites; and males compared with females. The dental caries risk is higher during pregnancy and lactation. All these trends have been described for MS as well. It suggests that MS and dental caries might both be caused in part by a dietary excess of certain fats and by vitamin D deficiency. Comparative epidemiology of multiple sclerosis and dental caries. Craelius W. J Epidemiol Community Health. 1978 Sep;32(3):155-65

Thomas E. Radecki, M.D., J.D.

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