There are two types of risk factors that are associated with the development of dementing conditions as we age. First, there are factors that we cannot control. The strongest risk factor for becoming demented is not directly controllable, age. If you live to be in your mid-80s or older, the risk is near 50%. There are other associated risk factors that are correlated with cognitive decline with aging such as apolipoprotein gene carrier status (Apoe4 has the greatest risk whereas Apoe2 has the least), Mild Cognitive Impairment, cancer (there is an inverse association between cancer and cognitive decline), and sex (women are at greater risk than men).
Second, there are also factors over which you have at least some degree of control. These include history of head injury (hence the desire to wear seatbelts and helmets), blood pressure at midlife and beyond, type II diabetes mellitus, stroke, exercise), smoking, drug and alcohol use.
Many believe, despite no good empirical evidence that dietary supplements such as vitamins may be neuroprotective. The latter is interesting as health problems are associated with either deficiency or excess concentrations, which is not a problem for most of us. A case in point is Vitamin D, there has been a recent surge in interest in vitamin D to promote brain health. Two recent findings from the Atherosclerosis Risk in Communities Study suggest that it is premature to take vitamin D to promote brain health.
First, the cognition study was published in the European Journal of Neurology in May 2014 based on analysis of 1650 participants. There was no association between lower levels of vitamin D and cognitive testing. Second, the MRI study was published in JAMA Neurology in May 2014 involving 1622 participants. Levels of vitamin D were not associated with white matter disease and did not prevent “subclinical” strokes.
It appears from past studies that there is an association of between low levels of vitamin D and hypertension, diabetes, heart attack, and stroke but this may just be a marker for poor health. It’s too early to recommend supplementation with vitamin D for those with normal blood levels as a “neuroprotective” strategy.
The relative risk of hypertension and cognitive decline is complex. An article in Neurology (2014, 82, 2187-2195) reports findings from the Age, Gene/Environment Susceptibility Reykjavik Study suggested that cognitive impairment in late life are dependent upon having a history of hypertension in midlife. Those with normal blood pressure in midlife had increased risk of white matter lesions and cerebral microbleeds if they experienced hypertension in late life. On the other hand, those with midlife hypertension had more brain atrophy and lower memory scores if they had lower late life diastolic blood pressure.
Finally, there is another recent study (Neurology, 2014) showing an inverse association between cancer and cognitive decline. There is no clear explanation of possible mechanism behind such a correlation.
The relationships between medical/life style factors and cognitive decline appear to be quit complex. The most proactive things we can do are to stay in shape, eat healthy, seek experiences, maintain health/wellness, and keep monitoring our short-term memory.