Year	mmol per litre
1980	4.314
1981	4.306
1982	4.297
1983	4.289
1984	4.279
1985	4.27
1986	4.259
1987	4.245
1988	4.227
1989	4.214
1990	4.204
1991	4.196
1992	4.19
1993	4.185
1994	4.183
1995	4.182
1996	4.183
1997	4.185
1998	4.188
1999	4.193
2000	4.202
2001	4.212
2002	4.223
2003	4.238
2004	4.253
2005	4.27
2006	4.289
2007	4.309
2008	4.326