Maybe you take some echinacea when you feel a cold coming on or sip a little chamomile tea to soothe an upset tummy. Smart moves. But which natural health boosters should you take regularly—and when?

The answers are extra important during tough financial times, when more and more Americans are buying vitamins and supplements as they struggle to afford traditional health care.

And because women are the biggest users of supplements, it’s critical that they know which ones really work. To make safe and effective buys, try this age-targeted advice from leading women’s-health experts.

Your 30s

Calcium You may not realize that your bone health starts waning in your late 30s. That means it’s never too early to maximize bone density with calcium, says Mary Jane Minkin, MD, clinical professor of obstetrics and gynecology at the Yale School of Medicine.

“Calcium may also ease menstrual cramps because it appears to regulate muscle contractions,” she says. Shoot for a total (through diet and supplements) of 1,000 milligrams a day during your 30s and 40s, and 1,200 to 1,500 in your 50s and beyond. Dr. Minkin recommends taking the cheapest brand that agrees with your stomach—the antacid TUMS E-X 750, whose active ingredient is calcium carbonate, works well and contains 300 milligrams of calcium per tablet ($5.49; Drugstore.com). If you love chocolate, try Viactiv; it contains 500 milligrams of calcium and just 20 calories per piece ($11.49).

Magnesium and Iron If you feel cranky at the end of your cycle, 200 milligrams of magnesium may help relax you, says Roberta Anne Lee, MD, vice chair of the Department of Integrative Medicine at Beth Israel Medical Center in New York City. But you don’t need to take it every day. Daily iron pills might make sense, experts say, because plenty of women are iron-deficient as they age; they either don’t get enough iron from their diets or are low because of blood loss during their periods. Ask your doc to check your iron level with a simple blood test. If it’s low, aim for 18 milligrams of iron a day to keep your energy up.