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Q: I’ve heard that you can’t absorb more than 500 milligrams of calcium at a time. So if I get 500 milligrams in a meal, will I get no benefit from taking a calcium supplement around the same time?

A: You’ll still absorb some of it. The more calcium you take in, the more you’ll absorb—though there’s a diminishing return. Keep in mind, your body absorbs only a small fraction of the calcium you consume, whether from food or supplements. And the more you get at one sitting, the smaller the proportion of it you absorb.

If you double your intake from 500 to 1,000 milligrams, for example, you don’t double the amount you absorb, though you do get more in total. With 500 milligrams of calcium, you’ll absorb about 30%, or 150 milligrams. But with 1,000 milligrams, you may absorb only 20%, or 200 milligrams. It’s okay that these percentages are small—scientists take absorption rates into consideration when determining recommended intake levels
for nutrients.

It’s still good advice to spread your calcium intake throughout the day, so you don’t exceed 500 milligrams at a time. But ultimately, it’s more important to make sure you reach your daily goal (1,000 to 1,200 milligrams), however you choose to get it, without worrying too much about the size or timing of the doses.

Q: Do vegetable oils need to be refrigerated?

A: Not for safety reasons. But refrigerated oils last longer. Natural antioxidants in vegetable oils help fight spoilage. Still, all oils eventually turn rancid, developing an off smell and taste. How soon this happens depends on the type of oil, how it has been processed, and how it is stored. While some oils have a shelf life of one or more years under normal conditions, natural or unrefined oils last only about four to six months.

To keep oil fresh longer:

• Keep it away from heat, light (keep it in a dark place or in an opaque container), and air (transfer oil to smaller containers as you use it). Seal tightly.

• Buy only what you will use within a few months. If you buy a larger size, you might want to refrigerate it. Chilled oils may form harmless crystals, which clear when the oil warms to room temperature.

• Flaxseed, sesame, and walnut oils have a short shelf life, so keep them refrigerated.

If your oil smells or tastes rancid, it won’t make you sick, but discard it anyway.

Q: What is a panic attack, and how can I be sure it isn’t a heart attack? How is it treated?

A: A panic attack is a sudden surge of fear and anxiety that usually comes out of nowhere. Symptoms may include sweating, nausea, chest pain, racing heartbeat, shortness of breath, dizziness, feeling faint, and a sense of impending doom. Most of these can also be caused by a heart attack. So unless you’ve had panic attacks before and are certain that’s what you’re experiencing, you should go to the emergency room if you have symptoms possibly related to a heart attack.

Once a heart attack and other medical problems have been ruled out, your doctor may refer you to a mental health professional for a diagnosis. Many people have one panic attack and never experience another, while others have repeated attacks that grow in frequency and intensity. If you’ve had multiple attacks, you may have a chronic condition called panic disorder, which, if untreated, can lead to phobias.

The underlying cause of panic attacks varies from person to person. Some experts believe the condition is largely psychological. Other factors that may play a role include heredity, significant stress in your life, and the side effects of some drugs (prescription or illegal ones) or dietary supplements. Women, especially after age 50, are more prone to attacks. In addition, some research has found an association between panic attacks and certain diseases, such as irritable bowel syndrome and mitral valve prolapse (a heart valve abnormality).

Because the causes and triggers vary, so do the treatments. Cognitive behavioral therapy helps many people. For others, antidepressants or tranquilizers, sometimes combined with psychotherapy, can be effective at reducing symptoms.

Q: How does goat’s milk compare to cow’s milk?

A: Advocates of goat’s milk claim that it is superior in many ways to cow’s milk. But nutritional differences between the two milks, if any, tend to be minor, according to USDA data. Goat’s milk is a little higher in calcium (330 milligrams per cup, versus 290 in cow’s milk), as well as protein and fat. It’s also higher in potassium, niacin, and vitamin A, for instance, but lower in vitamin B12, folate, and selenium. Neither cow’s milk nor goat’s milk is a particularly good source of many of these nutrients, anyway, and there’s no nutritional advantage to drinking one over the other. Both milks are fortified with vitamin D.

Some people claim that goat’s milk is less allergenic because of the structure of its proteins. But according to a review article this year in Pediatrics, studies indicate that children who are allergic to cow’s milk proteins are also likely to be allergic to goat’s milk proteins. It’s further claimed that because of its smaller fat globules ("naturally homogenized"), goat’s milk is more easily digested, whatever that means. Homogenization reduces the size of the fat globules in cow’s milk, too. Moreover, goat’s milk contains nearly as much lactose (milk sugar) as cow’s milk, so if you’re lactose-intolerant, goat’s milk is not the answer.

If you like its tangy taste, goat’s milk is a good source of calcium, protein, and other nutrients. But low-fat (and thus lower-calorie) versions are hard to find and usually cost more. Make sure any milk you drink is pasteurized; goat’s milk often is not.

Q: Walking up stairs or hills is good exercise, but what about walking down?

A: That’s good exercise, too. Going down stairs or hills takes less effort than going up, so it provides less of an aerobic workout, but it does strengthen the thigh muscles. Going up and down gives your leg muscles a more balanced workout by providing both concentric and eccentric exercise. That’s one reason why many stair-climber machines and elliptical trainers allow you to reverse your motion.

There are downsides to going down stairs or hills a lot: It’s more likely to cause delayed-onset muscle soreness. It can also be hard on your knees, so don’t overextend or lock your knees. Using walking poles while going downhill can reduce the strain.

UC Berkeley Wellness Letter, September 2010