DEAR DR. DONOHUE: Recently my granddaughter was hospitalized with water intoxication. She was in a catatonic state for two days and was hooked up to an IV with sodium because she had lost so much salt. Her electrolytes were all thrown off. She is an avid runner. Because so many of our youth are into sports, I thought it would be a good subject for you to write about. I understand this can be life-threatening. – A.M.

ANSWER: Your granddaughter had hyponatremia, a drop in her blood sodium level. It’s the opposite of dehydration. It comes from drinking too much plain water. Both dehydration and hyponatremia (water intoxication) happen in similar circumstances. They occur in hot weather when people are engaged in strenuous activity for long time periods. Or they can happen in situations where people sweat heavily, regardless of the weather.Was your granddaughter in a long-distance race? That’s the typical setting for hyponatremia. In the days before the condition was recognized, many marathon runners suffered from it. The overzealous drinking of plain water when people are sweating profusely leads to a profound drop in blood sodium. (Sodium is one of the body’s electrolytes. The other ones are potassium, chloride and bicarbonate.)

The drop in sodium, in turn, leads to water entering the brain and causing it to swell. That results in disorientation that can progress to confusion, seizures, coma and death. The replacement liquid for people who are sweating heavily for a long time should contain some salt.

Sports drinks fill that requirement. Putting half a teaspoon of salt and half a teaspoon of baking soda in a quart (about 1 liter) of water is another way to keep body sodium at the proper level. In anticipation of such circumstances, athletes should eat salty foods in the days before the event and have a salty snack two or three hours before it.

Thanks for telling people about your granddaughter’s experience. Water intoxication is a topic that demands more attention and recognition.

DEAR DR. DONOHUE: Every diet plan I read tells me to eat less. Several doctors have said I undereat and overexercise. I am 74, 4 feet 6 inches tall, and weigh 130 pounds. My usual calorie intake is 800 to 1,000 calories. I swim five to six hours a week and go to an exercise class for two hours a week. No one has ever told me how many calories I have to eat to lose weight. How many is that? – D.B.

ANSWER: For your height, your weight puts you in the slightly overweight category. Your body mass index – BMI (I calculated it for you) – is 26.2, and it should be 24.9 or less. It too indicates being slightly overweight. However, at older ages, neither body weight nor body mass index is a reliable indication of total health. Waist measurement is a better criterion. A woman’s waist should be less than 35 inches (89 cm) and a man’s, less than 40 inches (102 cm).Why are you struggling to lose weight? You really don’t need to. Your calorie intake is too low. It’s difficult to get proper nutrition with the number of calories you eat. You’re not getting enough vitamins and minerals. A woman of your height and your activity should eat roughly 1,900 calories a day.

I can’t explain why you don’t lose weight on your calorie intake. Have you had a physical examination? Perhaps your thyroid gland is sluggish and your metabolism has slowed down.

DEAR DR. DONOHUE: I am 5 feet, 10 inches tall and weigh 170 pounds. When I lie on my back, my belly is flat. When I stand up, it protrudes. What can I do? – D.P.

ANSWER: You can do two things. One is to exercise your stomach muscles so they act like a girdle. A good exercise is sit-ups done lying on your back with your lower legs on the seat of a chair. The other thing to do is to flatten the inward sway of your lower back. Stand against a wall and try to lessen the lower back’s inward curve. Practice regularly until that posture becomes habitual.

DEAR DR. DONOHUE: My granddaughter is 20. We have just been informed that she suffers from Marfan’s syndrome – something we know nothing about. The only thing that’s different about her is that she is taller than her brothers and sisters. Otherwise, she has been in fine health.We were told that this is inherited. No one in our family has or had it, and no one in my daughter-in-law’s family has it. How can it be inherited? What is it? – C.N.

ANSWER: Marfan’s is one of the most common inherited illnesses. When there is no family history of it, then a gene mutation occurred during the child’s early development in the uterus. Your granddaughter has a genetic disease, but, in her case, not an inherited one. About 25 percent of those with Marfan’s have it for the same reason your granddaughter has it.

Marfan’s signs and symptoms vary widely. Most of what I am going to describe might not apply to her. Marfan’s patients tend to be tall, with the lower part of the body being much longer than the upper part. They have an enormous arm span. Their fingers are slender and tapering.

Inner changes are the ones that cause problems. A wide aorta is an expected finding. The aorta is the large artery that sprouts directly from the heart. A Marfan’s aorta can develop a bulge (an aneurysm), and it can split apart – the most dangerous consequence of this syndrome. The eye’s lens often slips out of place. All this is intimidating, but the outlook for Marfan’s has changed immeasurably for the better, even for those who are most affected by it. Beta blocker medicines protect the aorta by decreasing the force with which blood is ejected into it from the heart. A close watch is kept on the aorta to see if it’s dangerously expanding. If it is, surgery can correct the defect.

None of this might apply to your granddaughter. She can expect a long and healthy life.