Year	mmol per litre
1980	5.373
1981	5.364
1982	5.348
1983	5.332
1984	5.318
1985	5.3
1986	5.284
1987	5.27
1988	5.251
1989	5.231
1990	5.211
1991	5.195
1992	5.185
1993	5.178
1994	5.172
1995	5.163
1996	5.155
1997	5.149
1998	5.144
1999	5.138
2000	5.128
2001	5.112
2002	5.087
2003	5.066
2004	5.047
2005	5.037
2006	5.032
2007	5.03
2008	5.026