Year	mmol per litre
1980	4.665
1981	4.654
1982	4.642
1983	4.633
1984	4.631
1985	4.627
1986	4.631
1987	4.634
1988	4.638
1989	4.644
1990	4.654
1991	4.665
1992	4.674
1993	4.684
1994	4.685
1995	4.691
1996	4.683
1997	4.671
1998	4.666
1999	4.662
2000	4.652
2001	4.645
2002	4.631
2003	4.632
2004	4.623
2005	4.614
2006	4.602
2007	4.592
2008	4.581