Year	mmol per litre
1980	4.64
1981	4.625
1982	4.609
1983	4.593
1984	4.576
1985	4.554
1986	4.533
1987	4.514
1988	4.497
1989	4.482
1990	4.466
1991	4.451
1992	4.434
1993	4.421
1994	4.407
1995	4.392
1996	4.379
1997	4.365
1998	4.353
1999	4.342
2000	4.33
2001	4.318
2002	4.303
2003	4.29
2004	4.279
2005	4.266
2006	4.255
2007	4.243
2008	4.231