Year	mmol per litre
1980	6.034
1981	6.022
1982	6.007
1983	5.992
1984	5.983
1985	5.969
1986	5.957
1987	5.939
1988	5.918
1989	5.892
1990	5.862
1991	5.827
1992	5.786
1993	5.748
1994	5.705
1995	5.666
1996	5.624
1997	5.583
1998	5.536
1999	5.493
2000	5.451
2001	5.415
2002	5.38
2003	5.348
2004	5.316
2005	5.284
2006	5.252
2007	5.222
2008	5.19