Year	mmol per litre
1980	4.781
1981	4.755
1982	4.732
1983	4.71
1984	4.685
1985	4.66
1986	4.64
1987	4.629
1988	4.619
1989	4.611
1990	4.606
1991	4.604
1992	4.6
1993	4.594
1994	4.586
1995	4.576
1996	4.567
1997	4.559
1998	4.551
1999	4.539
2000	4.529
2001	4.516
2002	4.505
2003	4.492
2004	4.478
2005	4.464
2006	4.446
2007	4.433
2008	4.418