Year	mmol per litre
1980	5.001
1981	4.984
1982	4.966
1983	4.947
1984	4.929
1985	4.911
1986	4.894
1987	4.875
1988	4.859
1989	4.84
1990	4.822
1991	4.796
1992	4.765
1993	4.733
1994	4.69
1995	4.647
1996	4.612
1997	4.578
1998	4.552
1999	4.524
2000	4.501
2001	4.482
2002	4.467
2003	4.453
2004	4.44
2005	4.425
2006	4.407
2007	4.393
2008	4.381