Year	mmol per litre
1980	4.386
1981	4.373
1982	4.36
1983	4.342
1984	4.323
1985	4.307
1986	4.288
1987	4.269
1988	4.25
1989	4.231
1990	4.211
1991	4.191
1992	4.172
1993	4.151
1994	4.136
1995	4.121
1996	4.109
1997	4.101
1998	4.095
1999	4.092
2000	4.088
2001	4.084
2002	4.079
2003	4.073
2004	4.067
2005	4.061
2006	4.054
2007	4.049
2008	4.044