Year	mmol per litre
1980	5.299
1981	5.28
1982	5.264
1983	5.249
1984	5.234
1985	5.217
1986	5.202
1987	5.183
1988	5.162
1989	5.139
1990	5.109
1991	5.077
1992	5.035
1993	4.983
1994	4.93
1995	4.875
1996	4.823
1997	4.78
1998	4.745
1999	4.716
2000	4.693
2001	4.674
2002	4.661
2003	4.652
2004	4.647
2005	4.646
2006	4.649
2007	4.654
2008	4.659