Year	mmol per litre
1980	4.656
1981	4.645
1982	4.637
1983	4.628
1984	4.618
1985	4.609
1986	4.597
1987	4.585
1988	4.573
1989	4.558
1990	4.541
1991	4.524
1992	4.503
1993	4.486
1994	4.459
1995	4.428
1996	4.397
1997	4.363
1998	4.335
1999	4.313
2000	4.292
2001	4.276
2002	4.264
2003	4.256
2004	4.249
2005	4.242
2006	4.237
2007	4.234
2008	4.23