Q: A reader recently mentioned that her doctor had suggested using bottled water because the water supply in her area was high in sodium. Are all bottled waters low in sodium?

A: No. There are more than 1,000 brands of bottled waters distributed internationally, and their sodium content does vary. In a recent issue of the journal of the American Dietetic Association, Georgette Koch of the New Jersey Department of Health reported on the sodium content of 33 mineral waters, 49 spring waters and nine other waters.

Among the mineral waters, 14 contained no more than 20 milligrams per liter, the optimal upper amount suggested by the Environmental Protection Agency. Seven had a maximum of more than 200 mg per liter, up to a high of 620 mg. Spring waters tended to have less; of the 49 varieties listed, only three contained more than 20 mg per liter, and the high was 71 mg per liter. The only three domestic kinds available nationwide -- Deer Park, Poland Spring and Mountain Valley -- all come in well below 10 mg per liter. Of the nine in the miscellaneous category, two contained very large amounts of sodium. One provided as much as 1,250 mg and the other a high of 1,677 mg in a liter.

The sodium content is now given on the labels of many bottled waters. If the brand you use does not provide this information, you have three choices. You can request the facts from the manufacturer, consult one of several paperbacks available that list sodium information about foods and beverages or switch to a brand whose label tells the story.

Q: I have recently developed diabetes and, unfortunately, I love sweets. Can you offer any guidance in preparing some of the cakes and cookies I miss?

A: We advise you to consult a source book containing dessert recipes interpreted in terms of the Diabetic Food Exchange System. This means that the recipe describes the number of other food exchanges such as bread, fruit, and fat you would consume out of your day's total in a single serving of dessert. One resource is the family cookbook series produced jointly by the American Diabetes Association and American Dietetic Association (ADA). Volume II was published in 1984 by Prentice Hall.

The diagnosis of diabetes is not necessarily synonymous with banishment of all desserts forever. If the condition is well controlled and the individual is at a desirable weight, occasional servings of dessert can be included in the diet regimen.

But most people who develop diabetes later in life are overweight, and losing weight is vitally important to controlling the condition. That means a program of increased physical activity and a low-calorie diet. Sad to say, if your diet is to be nutritionally adequate, there will probably be little room for the empty calories that are part of most desserts. Dietetic gelatin whipped with egg white and fruit is one of the few exceptions.

Since you have only recently been diagnosed as diabetic, we suggest asking your physician to recommend an ADA-registered dietitian to help you develop both a weight-loss plan and the adjustments needed to make your diet acceptable to you.

Q: I became concerned when I read that doses of Vitamin D as little as two or three times the Recommended Daily Allowance could be toxic. I am nursing an infant and am consuming five cups of milk a day, or 125 percent of the RDA for Vitamin D. I also take a supplement, which provides an additional 100 percent of RDA. Am I getting dangerous amounts?

A: No. Toxicity at levels of 1,000 IUs a day appears to be limited to a group of infants who are extremely sensitive to the vitamin. And it has been documented in children taking 10,000 IUs a day for as short a period as four months. Adults are less sensitive, so even though your need for Vitamin D is clearly being met both from your diet and, we presume, from some exposure to sunlight, the additional amount you are getting in a multivitamin supplement should pose no hazard.