Year	mmol per litre
1980	4.888
1981	4.882
1982	4.877
1983	4.866
1984	4.853
1985	4.836
1986	4.814
1987	4.788
1988	4.757
1989	4.728
1990	4.7
1991	4.677
1992	4.658
1993	4.641
1994	4.627
1995	4.613
1996	4.602
1997	4.594
1998	4.588
1999	4.585
2000	4.585
2001	4.584
2002	4.582
2003	4.586
2004	4.593
2005	4.597
2006	4.605
2007	4.614
2008	4.62