Year	mmol per litre
1980	4.651
1981	4.634
1982	4.617
1983	4.599
1984	4.581
1985	4.564
1986	4.547
1987	4.531
1988	4.517
1989	4.504
1990	4.492
1991	4.479
1992	4.466
1993	4.453
1994	4.442
1995	4.43
1996	4.419
1997	4.409
1998	4.399
1999	4.39
2000	4.381
2001	4.371
2002	4.356
2003	4.344
2004	4.332
2005	4.323
2006	4.314
2007	4.307
2008	4.302