Q. Is there a product containing both sunscreen and bug control (DEET) on the market? Are there any problems applying sunscreen and then 25 percent DEET spray? I want to be sensible and avoid both sunburn and mosquito bites.
A. Several combination products with both insect repellent and sunscreen are available. The Centers for Disease Control and Prevention don't recommend them because "sunscreen requires frequent applications while DEET should be used sparingly." Recent research shows another problem with such combination products (British Journal of Dermatology, June 2005). Mixing oxybenzone, a common sunscreen ingredient, with DEET dramatically increases absorption of both chemicals through the skin.
In addition, DEET can reduce the effectiveness of sunscreen applied at the same time (The Lancet, June 7, 1997). If you need both, apply your sunscreen first and allow it to dry before putting on the repellent. This reduces DEET absorption, though it may increase the passage of oxybenzone through the skin.
Q. I read in a magazine that the phosphoric acid in cola has an adverse effect on the absorption of calcium and vitamin D, increasing the chance of getting osteoporosis. Is this a major concern?
A. Studies have suggested that people who drink a lot of soda pop, especially cola, may be at higher risk of breaking bones later in life. Scientists wondered if this was due to the loss of calcium caused by caffeine or phosphoric acid in the soft drinks. To find out, researchers compared calcium lost in the urine after women drank water, milk or one of four different carbonated beverages, with and without caffeine, with and without phosphoric acid (American Journal of Clinical Nutrition, September 2001). They found that caffeine increased calcium loss, but phosphoric acid had no effect. The investigators concluded that the carbonated beverages are not a major cause of osteoporosis, but drinking soda instead of more nutritious beverages does represent a problem.
Q. I am desperate to get my thyroid back on track. I am miserable with symptoms of dry skin, constipation, depression, cold extremities and memory loss. My HMO will only approve generic levothyroxine, but it's not doing the job. What can I do?
A. At a recent meeting (May 23, 2005), the Food and Drug Administration concluded that all generic levothyroxine (T4) is equal to brand-name products like Synthroid or Levoxyl. There is research, however, that suggests some patients do better with additional T3 (another thyroid hormone) along with T4. You should not have to suffer with symptoms of low thyroid. We are sending you our Guide to Thyroid Hormones with a discussion of symptoms, test interpretation, interactions and balancing T3 and T4.
XIn their column, Joe and Teresa Graedon answer letters from readers. Write to them in care of King Features Syndicate, 888 Seventh Ave., New York, NY 10019, or e-mail them at firstname.lastname@example.org or via their Web site: www.peoplespharmacy.org.
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