Year	mmol per litre
1980	5.303
1981	5.292
1982	5.281
1983	5.271
1984	5.257
1985	5.245
1986	5.233
1987	5.214
1988	5.194
1989	5.17
1990	5.143
1991	5.111
1992	5.074
1993	5.045
1994	5.019
1995	4.994
1996	4.967
1997	4.94
1998	4.917
1999	4.892
2000	4.87
2001	4.851
2002	4.841
2003	4.826
2004	4.81
2005	4.799
2006	4.789
2007	4.785
2008	4.782