Year	mmol per litre
1980	4.558
1981	4.546
1982	4.527
1983	4.509
1984	4.489
1985	4.462
1986	4.44
1987	4.417
1988	4.393
1989	4.374
1990	4.356
1991	4.338
1992	4.32
1993	4.303
1994	4.287
1995	4.273
1996	4.26
1997	4.247
1998	4.237
1999	4.226
2000	4.215
2001	4.206
2002	4.196
2003	4.186
2004	4.175
2005	4.165
2006	4.156
2007	4.146
2008	4.136