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daily mul­ti­vi­ta­min “for in­sur­ance.” Wil­lett said that clin­i­cal tri­als un­der­es­ti­mate sup­ple­ments’ true ben­e­fits be­cause they aren’t long enough, of­ten last­ing five to 10 years. It could take decades to no­tice a lower rate of can­cer or heart dis­ease in vi­ta­min tak­ers, he said.

Vi­ta­min Users Start Out Health­ier

For Charlsa Bent­ley, 67, keep­ing up with the lat­est nu­tri­tion re­search can be frus­trat­ing. She stopped tak­ing cal­cium, for ex­am­ple, after stud­ies found it doesn’t pro­tect against bone frac­tures. Ad­di­tional stud­ies sug­gest that cal­cium sup­ple­ments in­crease the risk of kid­ney stones and heart dis­ease.

“I faith­fully chewed those cal­cium sup­ple­ments, and then a study said they didn’t do any good at all,” said Bent­ley, from Austin, Texas. “It’s hard to know what’s ef­fec­tive and what’s not.”

Bent­ley still takes five sup­ple­ments a day: a mul­ti­vi­ta­min to pre­vent dry eyes, mag­ne­sium to pre­vent cramps while ex­er­cis­ing, red yeast rice to pre­vent di­a­betes, coen­zyme Q10 for over­all health and vi­ta­min D based on her doc­tor’s rec­om­men­da­tion.

Like many peo­ple who take

di­etary sup­ple­ments, Bent­ley also ex­er­cises reg­u­larly — play­ing ten­nis three to four times a week — and watches what she eats.

Peo­ple who take vi­ta­mins tend to be health­ier, wealth­ier and bet­ter ed­u­cated than those who don’t, Kramer said. They are prob­a­bly less likely to suc­cumb to heart dis­ease or can­cer, whether they take sup­ple­ments or not. That can skew re­search re­sults, mak­ing vi­ta­min pills seem more ef­fec­tive than they re­ally are.

Faulty As­sump­tions

Preliminary find­ings can also lead re­searchers to the wrong con­clu­sions.

For ex­am­ple, sci­en­tists have long ob­served that peo­ple with high lev­els of an amino acid called ho­mo­cys­teine are more likely to have heart at­tacks. Be­cause folic acid can lower ho­mo­cys­teine lev­els, re­searchers once hoped that folic acid sup­ple­ments would pre­vent heart at­tacks and strokes.

In a se­ries of clin­i­cal tri­als, folic acid pills low­ered ho­mo­cys­teine lev­els but had no over­all ben­e­fit for heart dis­ease, Licht­en­stein said.

Stud­ies of fish oil also may have led re­searchers astray.

When stud­ies of large pop­u­la­tions showed that peo­ple who eat lots of seafood had fewer heart at­tacks, many as­sumed that the ben­e­fits came from the omega-3 fatty acids in fish oil, Licht­en­stein said.

Rig­or­ous stud­ies have failed to show that fish oil sup­ple­ments pre­vent heart at­tacks. A clin­i­cal trial of fish oil pills and vi­ta­min D, whose re­sults are ex­pected to be re­leased within the year, may pro­vide clearer ques­tions about whether they pre­vent dis­ease.

But it’s pos­si­ble the ben­e­fits of sar­dines and salmon have noth­ing to do with fish oil, Licht­en­stein said. Peo­ple who have fish for din­ner may be health­ier due to what they don’t eat, such as meat­loaf and cheese­burg­ers.

“Eat­ing fish is prob­a­bly a good thing, but we haven’t been able to show that tak­ing fish oil [sup­ple­ments] does any­thing for you,” said Dr. Steven Nis­sen, chair­man of car­dio­vas­cu­lar medicine at the Cleve­land Clinic Foun­da­tion.

Too Much Of A Good Thing?

Tak­ing mega­doses of vi­ta­mins and min­er­als, us­ing amounts that peo­ple could never con­sume through food alone, could be even more prob­lem­atic.

“There’s some­thing ap­peal­ing about tak­ing a nat­u­ral prod­uct, even if you’re tak­ing it in a way that is to­tally un­nat­u­ral,” Price said.

Early stud­ies, for ex­am­ple, sug­gested that beta carotene, a sub­stance found in car­rots, might help pre­vent can­cer.

In the tiny amounts pro­vided by fruits and veg­eta­bles, beta carotene and sim­i­lar sub­stances ap­pear to pro­tect the body from a process called ox­i­da­tion, which dam­ages healthy cells, said Dr. Edgar Miller, a pro­fes­sor of medicine at Johns Hop­kins School of Medicine.

Ex­perts were shocked when two large, well-de­signed stud­ies in the 1990s found that beta carotene pills ac­tu­ally in­creased lung can­cer rates. Like­wise, a clin­i­cal trial pub­lished in 2011 found that vi­ta­min E, also an an­tiox­i­dant, in­creased the risk of prostate can­cer in men by 17 per­cent. Such stud­ies re­minded re­searchers that ox­i­da­tion isn’t all bad; it helps kill bac­te­ria and ma­lig­nant cells, wip­ing them out be­fore they can grow into tu­mors, Miller said.

“Vi­ta­mins are not in­ert,” said Dr. Eric Klein, a prostate can­cer ex­pert at the Cleve­land Clinic who led the vi­ta­min E study. “They are bi­o­log­i­cally ac­tive agents. We have to think of them in the same way as drugs. If you take too high a dose of them, they cause side ef­fects.”

Gu­lati, the physi­cian in Phoenix, said her early ex­pe­ri­ence with recommending sup­ple­ments to her fa­ther taught her to be more cau­tious. She said she’s wait­ing for the re­sults of large stud­ies — such as the trial of fish oil and vi­ta­min D — to guide her ad­vice on vi­ta­mins and sup­ple­ments.

“We should be re­spon­si­ble physi­cians,” she said, “and wait for the data.”

KHN’s cov­er­age re­lated to aging and im­prov­ing care of older adults is sup­ported in part by The John A. Hart­ford Foun­da­tion.

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