Year	mmol per litre
1980	4.826
1981	4.789
1982	4.762
1983	4.737
1984	4.711
1985	4.688
1986	4.665
1987	4.644
1988	4.614
1989	4.589
1990	4.568
1991	4.541
1992	4.517
1993	4.492
1994	4.471
1995	4.453
1996	4.438
1997	4.425
1998	4.413
1999	4.405
2000	4.399
2001	4.391
2002	4.381
2003	4.372
2004	4.365
2005	4.354
2006	4.344
2007	4.336
2008	4.329