Year	mmol per litre
1980	4.592
1981	4.584
1982	4.58
1983	4.576
1984	4.571
1985	4.568
1986	4.562
1987	4.549
1988	4.54
1989	4.533
1990	4.53
1991	4.528
1992	4.526
1993	4.522
1994	4.514
1995	4.512
1996	4.502
1997	4.494
1998	4.486
1999	4.478
2000	4.468
2001	4.457
2002	4.442
2003	4.424
2004	4.406
2005	4.387
2006	4.37
2007	4.355
2008	4.338