Death rates where the underlying cause was Alzheimer's disease, Parkinson's disease or dementia have been considerably impacted by changes to coding rules, a new study has found.
Research on the trends in mortality from the three diseases between 1979 and 2004 by the Office for National Statistics (ONS) indicates that figures on death rates during this period may be misleading.
The study, conducted by Clare Griffiths and Cleo Rooney, also examined deaths from the cognitive illnesses that were not affected by coding changes, finding that death rates as a result of Alzheimer's disease grew by eight times for men and 12 times for women between 1985 and 2004.
However, this huge rise was partly attributed to the growing trend of recording Alzheimer's as the cause of death rather than dementia, as it is acknowledged that Alzheimer's is often the underlying cause of dementia.
In addition, it was discovered that mortality rates for Parkinson's disease fell by 22 per cent for males and 32 per cent for females over the same period.
The ONS has also recently revealed that dementia, including Alzheimer's disease, was the fourth highest cause of death among women in England and Wales during 2005 and the ninth leading cause for men.