Year	mmol per litre
1980	5.237
1981	5.23
1982	5.219
1983	5.207
1984	5.191
1985	5.171
1986	5.144
1987	5.113
1988	5.082
1989	5.051
1990	5.018
1991	4.99
1992	4.961
1993	4.934
1994	4.907
1995	4.88
1996	4.856
1997	4.836
1998	4.815
1999	4.794
2000	4.77
2001	4.748
2002	4.722
2003	4.698
2004	4.674
2005	4.652
2006	4.632
2007	4.612
2008	4.594