Year	mmol per litre
1980	5.363
1981	5.355
1982	5.346
1983	5.338
1984	5.326
1985	5.315
1986	5.304
1987	5.286
1988	5.266
1989	5.243
1990	5.216
1991	5.185
1992	5.15
1993	5.12
1994	5.096
1995	5.072
1996	5.048
1997	5.023
1998	5.005
1999	4.984
2000	4.966
2001	4.949
2002	4.938
2003	4.923
2004	4.908
2005	4.896
2006	4.886
2007	4.881
2008	4.876