Η λήψη βιταμινών και άλλων διατροφικών συμπληρωμάτων με ιχνοστοιχεία μετάλλων δεν φαίνεται να μειώνουν τον κίνδυνο καρκίνου ή καρδιοαγγειακών παθήσεων, σύμφωνα με μια νέα μεγάλη αμερικανική επιστημονική έρευνα, που αξιολόγησε τα έως τώρα στοιχεία. Η επιστημονική ετυμηγορία είναι ότι, προς το παρόν, είναι ανεπαρκή τα διαθέσιμα δεδομένα για να υποστηριχθεί πως αυτά τα σκευάσματα όντως έχουν ευεργετικό και προστατευτικό αποτέλεσμα, κάτι όμως που επίσης δεν μπορεί να αποκλεισθεί.
Εξαιτίας αυτής της αβεβαιότητας, η αρμόδια κυβερνητική επιστημονική επιτροπή των ΗΠΑ εξέδωσε μια σύσταση, που επιβεβαιώνει το προηγούμενο συμπέρασμά της από το 2003, ότι δηλαδή δεν είναι δυνατό να πάρει οριστική θέση ούτε κατά, ούτε υπέρ των πολυβιταμινών και των συμπληρωμάτων, όσον αφορά τα οφέλη τους για τον καρκίνο και την καρδιά.
Evidence for Supplement Use Lacking
There still is not enough evidence to recommend for or against using vitamin and mineral supplementation for the primary prevention of cardiovascular disease or cancer, a draft of updated recommendations from the U.S. Preventive Services Task Force (USPSTF) stated.
The task force also reaffirmed a recommendation against the use of beta-carotene supplements for preventing cardiovascular disease or cancer because of clear evidence of a lack of benefit, accompanied by an increased risk of lung cancer in those already at risk for the disease.
In a change from the previous iteration of the recommendations issued in 2003, the task force found enough evidence to advise against the use of vitamin E to protect against cardiovascular disease or cancer because of a lack of benefit.
The guidance applies to primary prevention in healthy adults without nutrient deficiencies, with the exception of women who are pregnant or may become pregnant, a group that “should take a daily supplement containing folic acid to help prevent neural tube defects.”
Sidney Smith Jr., MD, of the University of North Carolina at Chapel Hill, told MedPage Today that “information like this is very helpful in terms of informing us about the value of nutritional supplements.”
“I think we have to remember this deals with primary prevention, and my advice based on this and everything I’m seeing coming out is choose your diet wisely,” he said. “That’s the best thing you can do for cardiovascular health and cancer. And also be sure that if you have risk factors, you take medications that will deal with them effectively.”
The new proposed guidance is consistent with that from other organizations, including the National Institutes of Health and the Academy of Nutrition and Dietetics, which also found insufficient evidence to recommend the use of multivitamins to prevent chronic disease. The American Heart Association recommends “that healthy people get adequate nutrients by eating a variety of foods in moderation, rather than by taking supplements.”
The use of vitamins and minerals to prevent chronic disease has some biological plausibility based on the ability of certain supplements to counteract the oxidative stress and inflammation believed to be involved in the development of cardiovascular disease and cancer. And the general public appears to support the benefits of dietary supplements, with Americans spending $28.1 billion on them in 2010, according to the task force.
In 2003, the task force reviewed the evidence for use of vitamins A, C, and E, multivitamins with folic acid, and antioxidant combinations to prevent cardiovascular disease or cancer and determined that it was insufficient to recommend for or against their use for that purpose.
For the updated guidance, the task force considered an evidence review conducted by Stephen Fortmann, MD, of the Kaiser Permanente Center for Health Research in Portland, Ore., and colleagues and published online in Annals of Internal Medicine. In the new review, the researchers included a wider range of supplements, including vitamin D, calcium, selenium, and folic acid.
The findings led the task force to conclude that, overall, there was not enough evidence to make a determination on the relative risks and benefits or using multivitamins, single-nutrient supplements, or paired-nutrient supplements for the prevention of cardiovascular disease or cancer.
“However, there are only a limited number of studies for most individual nutrients, and differences in study designs make it difficult to pool effects across supplements,” according to the draft recommendations. “Therefore, the USPSTF is not able to conclude with certainty that there is no effect.”
The two exceptions were beta-carotene and vitamin E. With “moderate certainty,” the task force concluded that solid evidence indicated that neither supplement is effective at preventing cardiovascular disease and cancer, and that beta-carotene increases the risk of lung cancer in susceptible individuals.
Although pooled results from two trials — the Physicians’ Health Study II and the Supplementation in Vitamins and Mineral Antioxidants Study — did show a lower incidence of cancer among men taking multivitamins (pooled RR 0.94, 95% CI 0.89-1.00), there was no such benefit among women in the one study that included them.
That evidence was not strong enough to support a recommendation for using multivitamins to prevent cancer, however.
“Future trials should be more representative of the general population, including women and minority groups, and have enough power to demonstrate whether there are true subgroup differences,” the task force stated.
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Filed under: MEDICAL RESEARCH | Tagged: Evidence for Supplement Use Lacking, πολυβιταμίνες, Επιστημονική αβεβαιότητα για την προστατευτική δράση των πολυβιταμινών, βιταμίνες, Stephen Fortmann, vitamin |