Dr Thomas Stuttaford, the Times medical expert, is online every Wednesday. Submit your question about the new health topic of the week. If your question is published we like to include name and town/country. Please indicate if you would like to remain anonymous

Please note that Dr Tom isn't familiar with all the circumstances in individual cases and can only deal with the points raised in general terms. Patients should always discuss any specific problems they have with their own doctors.

Readers' questions are answered as examples of general problems commonly met in practice. It is a good rule in medicine that only their own doctors know the patient well enough to pontificate on the case as there are often other factors unknown to strangers.

Dr Tom answered questions recently (Feb 7, 2007) on dysmorphophobia (problems of body self image)

Can you explain the difference between Alzheimer's and dementia? My mother has just been diagnosed with the latter. N. Proby, Durham

Dementia is a symptom rather than a disease. There are many different conditions that can cause dementia of which the most common is Alzheimer's. The percentage of patients who suffer from Alzheimer's unalloyed with any other degenerative problem affecting the brain is estimated differently by experts. The probable number, as disclosed by the Framingham study in America that has analysed the medical history of a small town for many years, is that about 55 to 60 per cent of all cases of dementia can be attributed to Alzheimer's disease alone.

The other common cause of dementia is vascular dementia. This is the condition that used to be called multi infarct syndrome. With it the patient suffers a series of small strokes (infarcts) that do little damage in themselves, but the additive effect of repeated small strokes can result in a disability that is eventually as bad as that in severe Alzheimer's. About fifteen per cent of patients have dementia attributable to vascular causes. Another twelve per cent of patients suffer from both Alzheimer's and vascular dementia (multi infarct syndrome).

About eight per cent of those with dementia also have Parkinson's Disease. Dementia is also more common in patients with Parkinson's than in the population in general, and it is likely that another form of dementia, Lewey Body dementia, is also associated with Parkinson's. It and other miscellaneous causes including injury account for a further approximately ten per cent.

I have read recently two references to the importance of folic acid in keeping mentally alert in old age. Can you explain how this helps and also tell me how I can put this into my daily diet? I should add that I am adverse to taking a dietary complementary supplement if I can get the folic acid from regular foods, both on grounds of naturalness being best and, crucially, cost. Sean Flitton, Coventry

Folic acid has been recommended as a means of keeping the old mentally alert for years. The practice fell into abeyance but recent research has shown that it is useful. It is difficult to get enough folic acid to keep either Alzheimer's or congenital malformation in pregnant women at bay from natural sources alone. Yeast extracts is the best source followed by chicken livers, black eyed beans, soya, wheat germ, lamb's liver, asparagus, broccoli and Brussels sprouts. There is for instance ten times more folic acid in yeast extract than in Brussels sprouts and four times as much than in lamb's liver. The recommended dose is 400 micrograms a day - two of the standard tablets. As well as watching your diet so that it has plenty of folic acid and is low in fats you should have routine tests done to measure your blood pressure and your serum cholesterol levels.

Yes, I am lonely since my husband died. I am now 77. I live on my own and don't belong to any clubs, but I feel am too old to make the effort and start joining things. Also too shy. I feel trapped. I see my family rarely, they are young and busy and working. Name and address withheld

I am very sorry for you. You should ask at your local library, Citizens's Advice Bureau, Social Services department or, of course, your GP for clubs in the neighbourhood that would welcome you. In some areas social services or charities like Age Concern organise luncheon clubs, outings etc. I have known people of your age who have been widowed, and then have been initially too shy even to go shopping. When in general practice I used to arrange for someone to go with them into the shops for a few times until they had regained confidence.