Hg in red blood cells Men Women EPA in sera Men Women N Mean∗2 (ng/g) 95% CI N Mean∗2 (ng/g) 95% CI N Mean∗2 (mg/L) 95% CI N Mean∗2 (mg/L) 95% CI Men Women N Mean∗2 (mg/L) 95% CI N Mean∗2 (mg/L) 95% CI EPA in the HDL fraction of sera <69 26 41.9 70 24.3 26 68.3 70 57.3 26 25.0 71 21.1 Age 70–74 75–79 25 33.9 29 21.7 25 60.2 29 57.2 24 22.6 30 23.8 33.3–53.4 28.6–40.5 22.2–36.5 20.6 –29.0 16.4–29.5 13.7–23.0 54.0–87.6 45.3–81.7 42.8–75.5 25.4–48.0 51.4–64.1 47.6–69.3 46.1–64.8 41.3–56.6 19.9–32.0 16.8–32.0 20.0–35.6 12.0–21.7 18.8–23.7 20.2–28.2 17.1–25.6 16.1–22.9 Journal of Environmental and Public Health Table 1: Age speciﬁc concentrations of total mercury, EPA, and HDL-EPA. ∗1 : The continuous P for trend was calculated by treating age as a continuous variable. ∗2: Geometric mean. more strongly related to HDL EPA levels than serum EPA levels. Even if the notions described above are correct, it is dif- ﬁcult to explain the sex diﬀerence of the association between serum EPA and RBC-Hg levels. Note that, while EPA levels both in the serum and the HDL fraction of the serum were highly signiﬁcantly related to RBC-Hg levels among women, such an association was not observed among men. According to the survey of household spending, conducted by Japanese Ministry of Agriculture (Forestry and Fisheries white paper 2003), men aged 60 years or older tend to spend more money for eating out than for buying foods and groceries while women spend less for eating out. The types of ﬁsh which are consumed in home are saury, yellowtail, and horse mackerels. On the other hand, the types of ﬁsh which are consumed in food service industries are more heterogeneous, and they are tuna, shrimp, salmon, and trout, and so on. As shown in Table 4, men tended to eat dry ﬁsh more frequently than women. Most typical dry ﬁsh foods consumed by Japanese population uses horse mackerel and sardine, which belong to the bottom of the food chain and relatively high in EPA concentration. These observations suggest a possibility that men eat a variety of ﬁsh species that may have weak cor- relations between Hg and EPA contents in ﬁsh meats. The present study was conducted in a southern island in Japan, where ﬁsh consumption was considered to be relati- vely higher than the other areas in Japan. In the present study, geometric means of RBC-Hg level among men and women were 38.6 ng/g and 28.2 ng/g, respectively. They correspond to scalp hair mercury concentrations of 7.0 and 5.1 ppm, which were assuming that (i) the ratio of total mercury con- centrations in scalp hair (µg/g) to blood (µg/mL) is 250 [26]; (ii) the ratio between serum and RBC levels of total mercury is 0.264 [27]; (iii) hematocrit is about 40%. Those estimated mercury concentrations in scalp hair are higher than those in other areas of Japan [28], but similar to Wakisaka et al.’s study. They surveyed at the same area [29]. The relatively high mercury concentrations among men than among women, observed in the present study, were also reported from studies in Japan [28], probably reﬂecting sex diﬀerence in ﬁsh consumption. We used wet digestion method to measure total mercury levels. In human, unless occupational exposure to inorga- nic mercury is present, the major source of mercury is the 24 28.2 30 17.6 24 56.3 30 54.5 24 26.1 29 20.8 >80 23 23.7 17.8–32.4 42 21.7 18.0–26.4 23 34.4 42 48.2 21 15.9 40 19.1 3 P for trend∗1 <0.001 0.114 0.001 0.070 0.076 0.350