Year	mmol per litre
1980	4.603
1981	4.607
1982	4.608
1983	4.61
1984	4.611
1985	4.61
1986	4.604
1987	4.597
1988	4.589
1989	4.578
1990	4.57
1991	4.562
1992	4.552
1993	4.541
1994	4.533
1995	4.527
1996	4.522
1997	4.521
1998	4.517
1999	4.513
2000	4.508
2001	4.502
2002	4.496
2003	4.49
2004	4.483
2005	4.476
2006	4.467
2007	4.457
2008	4.447