Year	mmol per litre
1980	5.018
1981	4.996
1982	4.97
1983	4.947
1984	4.92
1985	4.897
1986	4.871
1987	4.845
1988	4.818
1989	4.788
1990	4.753
1991	4.714
1992	4.665
1993	4.621
1994	4.58
1995	4.537
1996	4.492
1997	4.459
1998	4.431
1999	4.405
2000	4.381
2001	4.36
2002	4.34
2003	4.323
2004	4.308
2005	4.296
2006	4.282
2007	4.269
2008	4.256