Year	mmol per litre
1980	5.318
1981	5.313
1982	5.306
1983	5.299
1984	5.289
1985	5.279
1986	5.268
1987	5.261
1988	5.254
1989	5.249
1990	5.245
1991	5.242
1992	5.241
1993	5.244
1994	5.243
1995	5.241
1996	5.238
1997	5.235
1998	5.23
1999	5.225
2000	5.22
2001	5.212
2002	5.205
2003	5.196
2004	5.187
2005	5.179
2006	5.171
2007	5.164
2008	5.157