Year	mmol per litre
1980	4.755
1981	4.723
1982	4.694
1983	4.666
1984	4.642
1985	4.621
1986	4.603
1987	4.588
1988	4.581
1989	4.574
1990	4.57
1991	4.567
1992	4.565
1993	4.565
1994	4.57
1995	4.575
1996	4.582
1997	4.592
1998	4.608
1999	4.628
2000	4.646
2001	4.663
2002	4.679
2003	4.693
2004	4.703
2005	4.711
2006	4.718
2007	4.724
2008	4.728