Year	mmol per litre
1980	5.615
1981	5.604
1982	5.591
1983	5.577
1984	5.567
1985	5.551
1986	5.538
1987	5.522
1988	5.502
1989	5.487
1990	5.462
1991	5.446
1992	5.438
1993	5.442
1994	5.452
1995	5.457
1996	5.458
1997	5.455
1998	5.443
1999	5.425
2000	5.404
2001	5.38
2002	5.346
2003	5.315
2004	5.288
2005	5.265
2006	5.238
2007	5.215
2008	5.193