Year	mmol per litre
1980	6.192
1981	6.186
1982	6.174
1983	6.159
1984	6.139
1985	6.121
1986	6.104
1987	6.08
1988	6.05
1989	6.019
1990	5.986
1991	5.951
1992	5.915
1993	5.88
1994	5.849
1995	5.816
1996	5.783
1997	5.756
1998	5.733
1999	5.712
2000	5.693
2001	5.673
2002	5.658
2003	5.644
2004	5.631
2005	5.619
2006	5.608
2007	5.595
2008	5.581