Year	mmol per litre
1980	5.024
1981	5.013
1982	5.001
1983	4.989
1984	4.972
1985	4.952
1986	4.931
1987	4.911
1988	4.893
1989	4.873
1990	4.858
1991	4.843
1992	4.832
1993	4.822
1994	4.816
1995	4.809
1996	4.8
1997	4.793
1998	4.784
1999	4.774
2000	4.767
2001	4.761
2002	4.756
2003	4.75
2004	4.743
2005	4.737
2006	4.731
2007	4.726
2008	4.721