Year	mmol per litre
1980	4.611
1981	4.603
1982	4.593
1983	4.582
1984	4.573
1985	4.564
1986	4.555
1987	4.548
1988	4.541
1989	4.537
1990	4.537
1991	4.54
1992	4.544
1993	4.55
1994	4.557
1995	4.564
1996	4.573
1997	4.584
1998	4.589
1999	4.594
2000	4.601
2001	4.611
2002	4.623
2003	4.636
2004	4.649
2005	4.663
2006	4.676
2007	4.692
2008	4.709