Year	mmol per litre
1980	4.524
1981	4.51
1982	4.497
1983	4.485
1984	4.476
1985	4.47
1986	4.461
1987	4.457
1988	4.454
1989	4.451
1990	4.446
1991	4.439
1992	4.427
1993	4.405
1994	4.379
1995	4.359
1996	4.345
1997	4.335
1998	4.33
1999	4.326
2000	4.323
2001	4.322
2002	4.325
2003	4.33
2004	4.336
2005	4.346
2006	4.359
2007	4.376
2008	4.394