DEAR DR. DONOHUE: I am a 43-year-old dentist who drinks two 2-liter diet pops a day. When possible, I drink the caffeine-free, but that’s a rarity. My twin 15-year-old daughters are constantly on me to stop drinking the diet pop. Convince them or me with medical data to stop. – J.M.

ANSWER: Whoa, doctor, that’s a lot of liquid – 1.04 gallons. How do you schedule patients between trips to the bathroom?

If a person drank eight 8-ounce glasses of water a day – the past, but no longer current, recommendation for daily water intake – it would amount to only half the fluid you drink. Furthermore, when you factor in fluids you get from other sources, even solid, dry-looking foods, you’re flooding yourself with liquid. I’m not saying it’s harmful, but it is excessive.

Phosphoric acid, found in many soft drinks, can draw calcium out of bones when huge amounts are drunk. Your amounts are huge.

Many caffeinated soft drinks contain 46 mg of caffeine in 12 ounces. Will you let me assume yours has a comparable amount? If it does – and you can check the list of ingredients – you are consuming about 500 mg of caffeine a day, close to five cups of coffee. Are you able to keep your hands steady when you’re manning the drill with that amount of caffeine circulating in your blood?

You are in a better position than I am to answer the question of carbonation’s effect on dental health. I’m not talking about ordinary amounts of carbonated beverages. I’m talking about big-league volumes such as yours. Some say that such large amounts can endanger tooth health, particularly if a person doesn’t practice good dental hygiene. On this issue, I’ll let you be the judge.

I side with your twins. I believe you have developed a habit that has the potential for some harm.

DEAR DR. DONOHUE: My daughter had West Nile fever last year. She caught it in a park while on a company picnic. Can she get it again? – D.

ANSWER: It’s nearly impossible to pick up a paper or listen to the evening news without being assaulted with a new and sinister threat to one’s health. West Nile virus is one of the latest medical conditions that cast a frightening specter.

The virus, known in Africa since the 1930s, first appeared in New York City in 1999. Since then, cases have been reported throughout the continental United States – a remarkably rapid spread of illness.

The virus is carried by birds and transmitted to humans through mosquito bites.

Most infections with the West Nile virus produce no symptoms. About a fifth of those infected come down with an illness that features fever, chills, headache, backache and joint pains. Many break out in a rash on the chest, back and arms. In a very few – usually older people – the virus infects the nervous system, and that sometimes leads to death.

The answer to your question is that having had one West Nile infection is believed to confer lifelong immunity. Your daughter should not be troubled by it ever again.

DEAR DR. DONOHUE: Moderate drinking of red wine is supposed to be good for general health. I have been told that grape juice does just as well. What do you think? – G.D.

ANSWER: Red wine and purple grape juice contain flavonoids – plant chemicals that keep cholesterol from sticking to artery walls.

All alcoholic beverages increase the level of HDL cholesterol – the good kind of cholesterol, the kind that helps prevent heart attacks. Grape juice, naturally, does not have this benefit. Fermentation makes flavonoids more absorbable, another point in wine’s favor. However, purple grape juice makes blood platelets less like to clump and, therefore, less likely to form a clot in a heart or brain artery.

DEAR DR. DONOHUE: My wife has had Parkinson’s for three years. She saw something on TV about a new med for it. Can you provide its name? – P.B.

ANSWER: Parkinson’s disease has many signs and symptoms, but one is burned in everyone’s mind – its tremor. The Parkinson’s tremor occurs with the hand resting in the lap. The tips of the thumb and index finger constantly roll against each other. Not every Parkinson’s patient has this tremor, but they all have one or more of the other Parkinson’s signs. Muscles affected by the illness are stiff. Bending the elbow can be accomplished only in a series of stops and starts. Many Parkinson’s patients take short, shuffling steps and are bent forward when they walk.

All Parkinson’s signs and symptoms come from a depletion of the brain chemical dopamine, which is essential for the movement centers of the brain to communicate with muscles.

Sinemet is a popular Parkinson’s drug. It restores the brain’s dopamine reserves. Requip, Mirapex, Permax and Parlodel are somewhat-recent additions to the Parkinson’s medicine chest. They act like dopamine. Even newer are Comtan and Tasmar, two medicines used in conjunction with Sinemet. Perhaps your wife heard of Apokyn, an injectable drug approved by the Food and Drug Administration in April 2004.

It provides some relief for the Parkinson’s patients who experience hypomotility – transient episodes when they cannot rise from a chair, speak or walk, or do all three. Surgical procedures like deep brain stimulation are also available for patients who don’t respond to drugs.