DEAR DR. DONOHUE: Is it important to have a bowel movement on a daily basis? A gastroenterologist told me that it is an old wives’ tale that you must have a daily bowel movement. He said I should not take stool softeners or laxatives to initiate a movement; I should do it naturally, no matter how difficult that is. He said that not having a movement for days is not harmful to my system.

This does not sound correct. I appreciate your comments. – W.G.

It isn’t necessary to have a daily bowel movement. Two criteria define constipation. One is stool frequency. Having fewer than three movements a week is one defining factor. Having to strain to eliminate hard stool is the other defining factor, regardless of frequency. In bygone years, people believed that a daily movement was needed to remove poisons from the body. That theory has been laid to rest and should be allowed to rest in peace.

A gradual increase in the amount of fiber a person eats can prevent constipation. Those in the know tell us to get 25 to 35 grams of fiber a day. Vegetables and fruits are good fiber sources – beans, peas and raspberries, to mention a few. Whole grains are another fiber bonanza. Whole grains are grains that haven’t been refined. They have their natural outer coat, bran. Bran is the fiber material. You can buy it at health-food stores if you can’t find whole-grain foods. Increase water intake when you increase your fiber intake.

Psyllium and methylcellulose are commercial fiber sources that you can turn to if you can’t get enough fiber from food. Metamucil is one brand name for psyllium, and Citrucel is a brand name for methylcellulose.

You can make your own natural remedy by adding prunes and 1 or 2 tablespoons of flaxseed (another health-food-store item) to a cup of yogurt.

Stool softeners – Colace is an example – are safe. Even laxatives aren’t scorned the way they used to be. Terrible consequences don’t stem from their occasional use. The booklet on constipation treats this national obsession in detail. Readers can obtain a copy by writing: Dr. Donohue – No. 504, Box 536475, Orlando, FL 32853-6475. Enclose a check or money order (no cash) for $4.75 U.S./$6 Can. with the recipient’s printed name and address. Please allow four weeks for delivery.

DEAR DR. DONOHUE: It’s reported that the best way to obtain vitamin D is through sunlight on skin. How much skin exposure, and for how long? When out for a walk or a bike ride, only the arms, legs and face are exposed. How long does it take to obtain the RDA for vitamin D? Can one get too much? – K.H.

Ultraviolet B rays, found in sunlight, convert a substance in the skin to a precursor of vitamin D, which is then turned into the actual vitamin by the kidneys and liver. During summer, only 15 minutes of sun exposure to the arms, legs and face, three times a week, provides the body with all the vitamin D it needs.

Older people are not as good at converting the skin material into vitamin D as young people are. And everyone living in the North rarely gets enough skin-made vitamin D in the winter. Vitamin D can be obtained from milk fortified with it. Eight ounces has 100 IU, as does 8 ounces of fortified orange juice. Salmon, 3.5 ounces, provides 360 IU, and the same amount of tuna has 200 IU. Multivitamins usually have 400 to 500 IU in each capsule.

The daily requirement for people over 71 is 600 IU; for those from 51 to 70, 400 IU; for adults 50 and younger, 400 IU. Many experts believe the daily intake should be 800 to 1,000 IU. The daily upper safe limit is 2,000 IU.

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