Year	mmol per litre
1980	5.524
1981	5.497
1982	5.471
1983	5.443
1984	5.414
1985	5.383
1986	5.349
1987	5.321
1988	5.294
1989	5.264
1990	5.24
1991	5.218
1992	5.195
1993	5.175
1994	5.166
1995	5.153
1996	5.145
1997	5.137
1998	5.135
1999	5.136
2000	5.136
2001	5.136
2002	5.14
2003	5.147
2004	5.159
2005	5.168
2006	5.181
2007	5.197
2008	5.214