Year	mmol per litre
1980	5.22
1981	5.175
1982	5.127
1983	5.079
1984	5.033
1985	4.984
1986	4.934
1987	4.886
1988	4.84
1989	4.796
1990	4.752
1991	4.707
1992	4.664
1993	4.623
1994	4.59
1995	4.563
1996	4.545
1997	4.534
1998	4.529
1999	4.53
2000	4.537
2001	4.548
2002	4.563
2003	4.581
2004	4.603
2005	4.626
2006	4.652
2007	4.678
2008	4.705