Year	mmol per litre
1980	5.419
1981	5.407
1982	5.396
1983	5.386
1984	5.375
1985	5.364
1986	5.35
1987	5.334
1988	5.315
1989	5.294
1990	5.268
1991	5.232
1992	5.183
1993	5.129
1994	5.069
1995	5.012
1996	4.961
1997	4.915
1998	4.869
1999	4.825
2000	4.787
2001	4.755
2002	4.733
2003	4.711
2004	4.696
2005	4.684
2006	4.675
2007	4.672
2008	4.669