written by Ted Schettler, MD, MPH
Today, a study in The Lancet reported that that the prevalence of dementia in the UK in 2011 was significantly lower than would have been expected based on the estimated prevalence in 1991. An accompanying editorial said, “A powerful message from these data is that what we as individuals and services do matters in terms of dementia. The CFAS data point to substantial added value from existing healthy lifestyle messages. They suggest that lifestyle changes—eg, in diet, exercise, and smoking—might reduce the risk of dementia and promote more general health and wellbeing.”
Many news outlets picked it up. See, for example, the BBC’s report. The story was also discussed on the News Hour with the lead, “Researchers See Decline in Dementia, Offering Optimism for Power of Lifestyle.”
A healthy lifestyle is of course important, but what has not been mentioned in any report that I’ve seen is the potential role of declining lead levels in the UK population.
The UK does not have a population-wide “NHANES-like” biomonitoring system. In the US, blood lead levels began to fall sharply when lead was phased out of gasoline. The UK began phasing lead out of gasoline in 1981. Attached below is a table from a paper showing lead levels in what was thought to be a fairly representative population of 2400 people in the UK in 1984. Of the 2400, about 1400 were considered most likely to be more highly exposed to gasoline. Presumably, levels have continued to fall since then.
Lead levels have fallen among workers in the UK in recent years ( See Morton J, Cotton R, Cocker J, Warren ND. Trends in blood lead levels in UK workers, 1995-2007. Occup Environ Med. 2010 Sep;67(9):590-5.)
Here are results of a 1984 biomonitoring project in which a total of nearly 2400 people were sampled. The geometric mean blood lead concentrations for the 4 main groups sampled are shown in Table 3.
From Quinn MJ, Delves HT. UK Blood Lead Monitoring Programme 1984-1987: protocol and results for 1984. Hum Toxicol. 1987 Nov;6(6):459-74:
Studies in the US show that higher lifetime levels of exposure to lead are associated with increased risk of cognitive decline and dementia. (see below)
I have no doubt that reduced smoking, increased exercise, and improved diet and blood pressure control are contributing to the unexpected findings reported today. We’ll never know for certain, but I suspect reductions in lead levels across the entire population are also playing a role in the dementia decrease, thirty years after it was phased out of gasoline.
Stewart WF, Schwartz BS. Effects of lead on the adult brain: a 15-year exploration. Am J Ind Med. 2007 Oct;50(10):729-39.
van Wijngaarden E, Campbell JR, Cory-Slechta DA. Bone lead levels are associated with measures of memory impairment in older adults. Neurotoxicology. 2009 Jul;30(4):572-80
Bandeen-Roche K, Glass TA, Bolla KI, Todd AC, Schwartz BS. Cumulative lead dose and cognitive function in older adults. Epidemiology. 2009 Nov;20(6):831-9.
Shih RA, Glass TA, Bandeen-Roche K, Carlson MC, Bolla KI, Todd AC, Schwartz BS. Environmental lead exposure and cognitive function in community-dwelling older adults. Neurology. 2006 Nov 14;67(9):1556-62.
Peters JL, Weisskopf MG, Spiro A 3rd, Schwartz J. Interaction of stress, lead burden, and age on cognition in older men: the VA Normative Aging Study. Environ Health Perspect. 2010 Apr;118(4):505-10.