Year	mmol per litre
1980	5.326
1981	5.326
1982	5.323
1983	5.317
1984	5.312
1985	5.31
1986	5.305
1987	5.298
1988	5.285
1989	5.266
1990	5.25
1991	5.233
1992	5.207
1993	5.178
1994	5.152
1995	5.13
1996	5.108
1997	5.083
1998	5.059
1999	5.033
2000	5.007
2001	4.985
2002	4.968
2003	4.951
2004	4.935
2005	4.922
2006	4.912
2007	4.907
2008	4.903