Year	mmol per litre
1980	5.004
1981	4.978
1982	4.951
1983	4.922
1984	4.893
1985	4.864
1986	4.837
1987	4.808
1988	4.78
1989	4.754
1990	4.727
1991	4.705
1992	4.684
1993	4.662
1994	4.644
1995	4.626
1996	4.61
1997	4.601
1998	4.594
1999	4.592
2000	4.595
2001	4.594
2002	4.592
2003	4.592
2004	4.592
2005	4.594
2006	4.596
2007	4.599
2008	4.601