Year	mmol per litre
1980	4.338
1981	4.33
1982	4.321
1983	4.307
1984	4.294
1985	4.276
1986	4.262
1987	4.25
1988	4.242
1989	4.238
1990	4.234
1991	4.236
1992	4.235
1993	4.237
1994	4.24
1995	4.241
1996	4.241
1997	4.241
1998	4.246
1999	4.251
2000	4.257
2001	4.267
2002	4.277
2003	4.286
2004	4.296
2005	4.306
2006	4.313
2007	4.321
2008	4.329