Cancer mortality and other causes of death in users of geothermal hot water

Figures & data

Figure 1. Map of Iceland showing the age of the bedrock, dark area: age of bedrock less than 0.8 million years, grey area: age of bedrock 0.8–3.3 million years, light grey area: age of bedrock 3.3–15 million years, and white area: glaciers. Modified with permission from Iceland GeoSurvey – ÍSOR.

Figure 2. Map of Iceland showing the study areas: 1) Geothermal heating area, two enlarged parts with community codes, 2) Cold reference area, 3) Warm reference area, 4) Capital and South West area, and 5) Uninhabited area. Modified with permission from National Land Survey of Iceland.

Table I. Baseline characteristics in the geothermal heating area and the two reference areas according to census 1981.

	Geothermal heating area N (%)	Warm reference area N (%)	Cold reference area N (%)
Number of people	7511 (100)	44 864 (100)	22 431 (100)
Gender
Men	3893 (51.8)	23 305 (51.9)	11 929 (53.2)
Woman	3618 (48.2)	21 559 (48.1)	10 502 (46.8)
Age, year
Mean± SD	28.30 ± 16.35	28.14 ± 16.30	28.06 ± 16.20
Median, IQR (0.25; 0.75)	26 (15; 40)	25 (15; 40)	25 (15; 39)
Education
Basic education	1829 (24.3)	12 370 (27.6)	6565 (29.3)
Medium education	2088 (27.8)	11 754 (26.2)	5665 (25.3)
Academic education	622 (8.3)	3171 (7.1)	1428 (6.4)
Unclassified	2878 (38.3)	17 061 (38.0)	8481 (37.7)
Missing	94 (1.3)	508 (1.1)	292 (1.3)
Housing
Single family home	5730 (76.3)	29 236 (65.2)	17 343 (77.3)
Other type of house	1781 (23.7)	15 628 (34.8)	5088 (22.7)
Region
Urban regions ≥ 500 individuals	5793 (77.1)	30 554 (68.1)	12 839 (57.2)
Rural regions < 500 individuals	1718 (22.9)	14 310 (31.9)	9592 (42.8)

IQR, interquartile range; SD, standard deviation.

Figure 3. Kaplan-Meier estimates of event-free proportion for death since the census 1981, dashed line indicate population in geothermal water area, and black line population in the combined reference areas, (A) breast cancer death (Log-rank test: p = 0.006), (B) prostate cancer death (Log-rank test: p < 0.000), (C) non-Hodgkin's lymphoma death (Log-rank test: p = 0.011), and (D) suicide (Log-rank test: p = 0.004).

Table II. Number of all causes of death and selected causes of death among men and women separately in the geothermal heating area, hazard ratio (HR), 95% confidence intervals (CI) according to comparison with the reference areas combined, adjusted for age, education, type of housing, and smoking habits. Statistically significant HRs are in bold.

	Geothermal heating area	Cold and warm reference areas combined
	p-yr 96 294	p-yr 882 022
Causes of death (ICD-10)	No. of deaths	No. of deaths	HR	95% CI
Men
All causes (A00–Y98)	596	5536	1.00	0.91–1.08
All Neoplasms (C00–C97 and D45–D47)	193	1687	1.06	0.91–1.23
Prostate (C61)	47	239	1.88	1.37–2.60
Lymphoid and haematopoietic tissue (C81–C96 and D45–D47)	20	162	1.20	0.75–1.93
Non-Hodgkin's lymphoma (C82–C85)	12	45	2.31	1.21–4.41
Immunoproliferative diseases (C88)	1	6	1.35	0.16–11.57
Diseases of the respiratory system (J00–J99)	32	344	0.92	0.64–1.32
Influenza (J10–J11)	5	17	3.10	1.09–8.84
All external causes (V01–Y98)	74	656	1.04	0.82–1.33
Suicide and intentional self-harm (X60–X84)	31	190	1.46	1.00–2.13
	p-yr 91 896	p-yr 822 346
Women
All causes ICD-10	400	3570	1.00	0.90–1.11
All Neoplasms (C00–C97 and D45–D47)	167	1386	1.04	0.89–1.23
Breast (C50)	40	230	1.49	1.06–2.09
Lymphoid and haematopoietic tissue (C81–C96 and D45–D47)	18	104	1.49	0.89–2.47
Non-Hodgkin's lymphoma (C82–C85)	4	28	1.53	0.52–4.46
Immunoproliferative diseases (C88)	2	2	8.39	1.15–61.42
Diseases of the respiratory system (J00–J99)	38	289	1.20	0.85–1.70
Influenza (J10–J11)	4	11	3.99	1.21–13.18
All external causes (V01–Y98)	29	184	1.41	0.95–2.10
Suicide and intentional self-harm (X60–X84)	10	39	2.05	1.02–4.15

p-yr, person years.