Year	mmol per litre
1980	5.026
1981	5.016
1982	5.003
1983	4.991
1984	4.979
1985	4.97
1986	4.961
1987	4.955
1988	4.948
1989	4.943
1990	4.939
1991	4.936
1992	4.934
1993	4.933
1994	4.933
1995	4.933
1996	4.932
1997	4.93
1998	4.929
1999	4.928
2000	4.927
2001	4.925
2002	4.921
2003	4.917
2004	4.911
2005	4.905
2006	4.897
2007	4.888
2008	4.879