Year	mmol per litre
1980	6.243
1981	6.211
1982	6.179
1983	6.15
1984	6.123
1985	6.101
1986	6.081
1987	6.061
1988	6.037
1989	6.014
1990	5.99
1991	5.969
1992	5.94
1993	5.914
1994	5.885
1995	5.855
1996	5.822
1997	5.79
1998	5.769
1999	5.748
2000	5.724
2001	5.702
2002	5.679
2003	5.653
2004	5.63
2005	5.607
2006	5.587
2007	5.567
2008	5.547