Year	mmol per litre
1980	5.082
1981	5.067
1982	5.05
1983	5.033
1984	5.017
1985	5.001
1986	4.986
1987	4.969
1988	4.951
1989	4.93
1990	4.908
1991	4.885
1992	4.865
1993	4.846
1994	4.826
1995	4.809
1996	4.792
1997	4.774
1998	4.757
1999	4.741
2000	4.731
2001	4.719
2002	4.707
2003	4.696
2004	4.684
2005	4.675
2006	4.668
2007	4.662
2008	4.658