Year	mmol per litre
1980	5.109
1981	5.092
1982	5.074
1983	5.056
1984	5.038
1985	5.018
1986	5
1987	4.981
1988	4.961
1989	4.938
1990	4.912
1991	4.88
1992	4.843
1993	4.806
1994	4.761
1995	4.717
1996	4.674
1997	4.629
1998	4.592
1999	4.565
2000	4.547
2001	4.535
2002	4.527
2003	4.526
2004	4.53
2005	4.535
2006	4.539
2007	4.541
2008	4.542