Year	mmol per litre
1980	4.414
1981	4.412
1982	4.41
1983	4.407
1984	4.405
1985	4.402
1986	4.399
1987	4.396
1988	4.391
1989	4.389
1990	4.386
1991	4.383
1992	4.383
1993	4.385
1994	4.389
1995	4.395
1996	4.401
1997	4.408
1998	4.417
1999	4.428
2000	4.438
2001	4.449
2002	4.461
2003	4.475
2004	4.488
2005	4.5
2006	4.514
2007	4.528
2008	4.544