Year	mmol per litre
1980	5.315
1981	5.311
1982	5.302
1983	5.292
1984	5.279
1985	5.261
1986	5.239
1987	5.213
1988	5.187
1989	5.16
1990	5.13
1991	5.105
1992	5.079
1993	5.055
1994	5.03
1995	5.005
1996	4.982
1997	4.96
1998	4.938
1999	4.914
2000	4.889
2001	4.865
2002	4.839
2003	4.813
2004	4.789
2005	4.764
2006	4.74
2007	4.717
2008	4.693