Year	mmol per litre
1980	5.075
1981	5.071
1982	5.066
1983	5.059
1984	5.05
1985	5.039
1986	5.029
1987	5.024
1988	5.014
1989	5.002
1990	4.992
1991	4.953
1992	4.926
1993	4.909
1994	4.896
1995	4.88
1996	4.876
1997	4.867
1998	4.871
1999	4.883
2000	4.893
2001	4.906
2002	4.916
2003	4.91
2004	4.906
2005	4.901
2006	4.897
2007	4.895
2008	4.892