Year	mmol per litre
1980	4.466
1981	4.437
1982	4.409
1983	4.378
1984	4.348
1985	4.318
1986	4.293
1987	4.268
1988	4.247
1989	4.228
1990	4.215
1991	4.205
1992	4.2
1993	4.197
1994	4.196
1995	4.197
1996	4.199
1997	4.207
1998	4.215
1999	4.223
2000	4.23
2001	4.24
2002	4.25
2003	4.259
2004	4.272
2005	4.285
2006	4.297
2007	4.31
2008	4.324