Year	mmol per litre
1980	4.429
1981	4.416
1982	4.404
1983	4.39
1984	4.376
1985	4.364
1986	4.351
1987	4.339
1988	4.33
1989	4.322
1990	4.315
1991	4.307
1992	4.3
1993	4.292
1994	4.286
1995	4.28
1996	4.274
1997	4.268
1998	4.263
1999	4.258
2000	4.253
2001	4.249
2002	4.239
2003	4.233
2004	4.228
2005	4.224
2006	4.221
2007	4.219
2008	4.22