Year	mmol per litre
1980	4.946
1981	4.936
1982	4.927
1983	4.921
1984	4.916
1985	4.909
1986	4.907
1987	4.911
1988	4.918
1989	4.925
1990	4.934
1991	4.942
1992	4.949
1993	4.957
1994	4.965
1995	4.974
1996	4.975
1997	4.976
1998	4.976
1999	4.978
2000	4.982
2001	4.988
2002	4.994
2003	5
2004	5.006
2005	5.012
2006	5.016
2007	5.02
2008	5.024