Year	mmol per litre
1980	6.064
1981	6.049
1982	6.031
1983	6.013
1984	5.993
1985	5.973
1986	5.958
1987	5.938
1988	5.925
1989	5.913
1990	5.894
1991	5.877
1992	5.855
1993	5.836
1994	5.816
1995	5.799
1996	5.782
1997	5.768
1998	5.758
1999	5.745
2000	5.736
2001	5.73
2002	5.72
2003	5.71
2004	5.701
2005	5.696
2006	5.688
2007	5.681
2008	5.674