Year	mmol per litre
1980	4.409
1981	4.4
1982	4.391
1983	4.379
1984	4.369
1985	4.355
1986	4.341
1987	4.326
1988	4.314
1989	4.301
1990	4.291
1991	4.281
1992	4.277
1993	4.271
1994	4.264
1995	4.26
1996	4.267
1997	4.295
1998	4.326
1999	4.365
2000	4.402
2001	4.449
2002	4.495
2003	4.536
2004	4.579
2005	4.615
2006	4.641
2007	4.664
2008	4.684