Year	mmol per litre
1980	4.562
1981	4.545
1982	4.528
1983	4.51
1984	4.489
1985	4.468
1986	4.447
1987	4.427
1988	4.408
1989	4.389
1990	4.371
1991	4.353
1992	4.335
1993	4.319
1994	4.302
1995	4.288
1996	4.275
1997	4.264
1998	4.256
1999	4.247
2000	4.238
2001	4.231
2002	4.222
2003	4.214
2004	4.203
2005	4.192
2006	4.181
2007	4.168
2008	4.157