Year	mmol per litre
1980	5.031
1981	5.027
1982	5.024
1983	5.02
1984	5.017
1985	5.015
1986	5.009
1987	4.997
1988	4.983
1989	4.962
1990	4.939
1991	4.905
1992	4.861
1993	4.809
1994	4.763
1995	4.731
1996	4.718
1997	4.717
1998	4.722
1999	4.729
2000	4.741
2001	4.752
2002	4.76
2003	4.761
2004	4.761
2005	4.759
2006	4.755
2007	4.754
2008	4.752