Year	mmol per litre
1980	4.773
1981	4.756
1982	4.739
1983	4.718
1984	4.695
1985	4.674
1986	4.652
1987	4.631
1988	4.608
1989	4.587
1990	4.563
1991	4.539
1992	4.516
1993	4.491
1994	4.469
1995	4.448
1996	4.43
1997	4.413
1998	4.398
1999	4.385
2000	4.371
2001	4.356
2002	4.34
2003	4.324
2004	4.307
2005	4.29
2006	4.272
2007	4.255
2008	4.239