The study, involving nearly 1,000 children aged 3 months to 4 years, provides evidence against the popular and costly use of probiotics -- live microorganisms believed to restore the balance of intestinal bacteria and boost the immune system.
"Probiotics had no effect on the children. Parents are better off saving their money and using it to buy more fresh fruits and vegetables for their children," said study co-author, Phillip Tarr, Professor at Washington University School of Medicine in St. Louis.
The findings, published in the New England Journal of Medicine, showed that a commonly used probiotic is not effective in improving symptoms in young patients with gastroenteritis, popularly known as "stomach flu".
The researchers evaluated a common probiotic known as Lactobacillus rhamnosus GG, or LGG, which is sold over the counter as Culturelle. Certain versions of the probiotic are intended for babies and children.
There are no treatments for pediatric acute gastroenteritis other than giving children fluids to prevent dehydration and, sometimes, medication to relieve nausea. The lack of options has prompted some physicians and parents to give ill children probiotics, the researchers said.
The study, published in the Journal of Adolescent Health, found that these types of supplements were linked to nearly three times as many severe medical outcomes in young people.
"The FDA has issued countless warnings about supplements sold for weight loss, muscle building or sport performance, sexual function, and energy, and we know these products are widely marketed to and used by young people. So what are the consequences for their health? That's the question we wanted to answer," said lead author Flora Or from Harvard University.
For the study, the researchers looked at adverse event reports between January 2004 and April 2015 in the US and analysed the relative risk for severe medical events such as death, disability and hospitalisation in individuals aged zero and 25 years that were linked with the use of dietary supplements sold for weight loss, muscle building, or energy compared to vitamins.
They found that there were 977 single-supplement-related adverse event reports for the target age group. Of those, approximately 40 per cent involved severe medical outcomes, including death and hospitalisation.
Supplements sold for weight loss, muscle building and energy were associated with almost three times the risk for severe medical outcomes compared to vitamins, said the study.
"Many of these products have been found to be adulterated with prescription pharmaceuticals, banned substances, heavy metals, pesticides and other dangerous chemicals" said S. Bryn Austin, Professor at Harvard University.
According to the study published in the journal Annals of Internal Medicine, supplements combining calcium and vitamin D may be linked to a slightly increased stroke risk.
However, there was no evidence that calcium or vitamin D taken alone had any health risks or benefits.
"Our analysis carries a simple message that although there may be some evidence that a few interventions have an impact on death and cardiovascular health, the vast majority of multivitamins, minerals and different types of diets had no measurable effect on survival or cardiovascular disease risk reduction," said study lead author Safi U. Khan, Assistant Professor at the West Virginia University.
For the study, the researchers used data from 277 randomised clinical trials that evaluated 16 vitamins or other supplements and eight diets for their association with mortality or heart conditions including coronary heart disease, stroke and heart attack.
They included data gathered on 992,129 research participants worldwide.
The analysis showed possible health benefits only from a low-salt diet, omega-3 fatty acid supplements and possibly folic acid supplements for some people.
"The panacea or magic bullet that people keep searching for in dietary supplements isn't there," said senior author of the study Erin Michos from Johns Hopkins University School of Medicine in the US.
"People should focus on getting their nutrients from a heart-healthy diet, because the data increasingly show that the majority of healthy adults don't need to take supplements," Michos said.
According to Abhishek Singh, Consultant Cardiologist at Columbia Asia Hospital in Ghaziabad, dietary supplements do not have a measurably positive impact on cardiac health.
"It's more important to follow a healthy dietary regimen and avoid foods that are bad for the heart. Trans fatty acids are harmful and have to be curtailed. Refined sugars and simple carbohydrates are to be kept at a minimum," Singh told IANS.
The doctor suggested that people should include more green vegetables in their diet. They are rich in vitamin K and dietary nitrates, which help protect the arteries and reduce blood pressure, he said.
"Studies like this raise concerns about harm from calcium and Vitamin D supplement use. As far as Vitamin D supplements (without calcium) are concerned, there has been no evidence on whether it has any impact on cardiovascular disease risk reduction," Anupama Singh, Senior Consultant, Internal Medicine at Vimhans Nayati Super Specialty Hospital in Delhi, told IANS.
"The quality of the evidence base of these various nutritional supplements and dietary interventions still needs to be evaluated to ascertain the effectiveness of the study," she added.
According to the study, published in the journal Nutrients, public health officials should issue a clear set of nutritional recommendations to complement messages about the role of handwashing and vaccinations in preventing the spread of infections.
"There's a wealth of data that shows the role that good nutrition plays in supporting the immune system. As a society, we need to be doing a better job of getting that message across along with the other important, more common messages," said study researcher Adrian Gombart from Oregon State University in the US.
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Specific vitamins, minerals, and fatty acids have key jobs to play in helping your immune system, Gombart said. In particular vitamin C, vitamin D, zinc, and an omega-3 fatty acid found in fish, docosahexaenoic acid, also known as DHA, are critical for immune function.
The roles that vitamins C and D play in immunity are particularly well known.
According to the researchers, vitamin C has roles in several aspects of immunity, including the growth and function of immune cells and antibody production.
"Vitamin D receptors on immune cells also affect their function. This means that vitamin D profoundly influences your response to infections," Gombart said.
"The problem is that people simply aren't eating enough of these nutrients. This could destroy your resistance to infections. Consequently, we will see an increase in disease and all of the extra burdens that go along with that increase," he added.
That's why the researchers are urging not only a daily multivitamin, but doses of 200 milligrams or more of vitamin C (higher than the suggested federal guidelines of 75 milligrams for men and 50 for women) and 2,000 international units of vitamin D, rather than the 400 to 800 recommended depending on age.
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There is no doubt that vaccines, when available, can be effective, but they're not foolproof, Athe researchers noted. The other collaborators of the study were the University of Southampton (United Kingdom), the University of Otago (New Zealand), and University Medical Center (The Netherlands).
(IANS)