Year	mmol per litre
1980	5.68
1981	5.644
1982	5.607
1983	5.573
1984	5.542
1985	5.513
1986	5.483
1987	5.456
1988	5.432
1989	5.412
1990	5.394
1991	5.376
1992	5.361
1993	5.348
1994	5.335
1995	5.322
1996	5.31
1997	5.299
1998	5.29
1999	5.282
2000	5.276
2001	5.275
2002	5.276
2003	5.28
2004	5.282
2005	5.288
2006	5.296
2007	5.31
2008	5.323