Experts take issue with researchers' conclusion that supplements don't prevent death

A team of researchers from Tufts University combed through data from rounds of the National Health and Nutrition Examination Survey from 1999 through 2009.  Their study was published this week in the journal Annals of Internal Medicine​​​.

Excluding pregnant and lactating women, the researchers came up with a data set that included answers to the questionnaires from more than 30,000 participants.  The researchers were looking to see what the risks and benefits of supplements were when looking at all mortality endpoints. 

“We evaluated the association between dietary supplement use and mortality from all causes, cardiovascular disease (CVD), and cancer. We further assessed whether adequate or excess nutrient intake was associated with mortality and whether the associations differed by nutrient intake from foods versus supplements,” ​they wrote.

Of the participants, about 71% were classified as white, 11% were listed as non-Hispanic black, and about 13% were Hispanic. Slightly more than half of the respondents reported using a supplement in the prior 30 days, with about 38% having used a multivitamin/mineral supplement.

Supplement group older, with more health concerns

The group that reported as supplement users averaged about 50 years old, while the non supplement users were younger, coming in at about 43 years old.  The supplement users group had higher rates of cancer, high cholesterol and hypertension, which could be attributed to the age difference between the groups.

The researchers did address some of the problems associated with dealing with such a large and amorphous population group. Supplement use was subject to recall bias, they noted, though they did say that information from labels of products was captured at the time of the interviews. They also noted that the nutrient intakes were arrived at via the self-reported intakes and could be subject to error.  

And they noted that multiple nutrients were evaluated in the study, including a full suite of vitamins and minerals, the carotenoids lutein, zeaxanthin and lycopene and EPA and DHA as well as dietary fiber. 

Confounders controlled for

Even with the multiple confounders, the researchers were confident that these had been adequately controlled for.

“Having chronic health conditions, such as cancer, CVD, hypertension, or diabetes, may also motivate initiation of dietary supplement use. To minimize the chance of residual confounding, we adjusted for all of these factors in the multivariable models. In addition, we stratified participants by presence of comorbid conditions at baseline, and the associations remained similar,” ​they wrote.

The researchers concluded that dietary supplement use did not prevent premature death.  They also noted risks associated with some excess nutrient intakes, such as a link of too much calcium intake with a heightened risk of some cancers.

“In conclusion, use of dietary supplements was not associated with mortality benefits among a nationally representative sample of US adults. Although adequate nutrient intake from foods could contribute to reduced risk for death, excess intake from supplements might increase mortality,”​ they wrote.

Preventing death, or promoting health?

Andrew Shao, PhD, acting senior vice president of scientific and regulatory affairs for the Council for Responsible Nutrition said the results needed to be taken seriously, as NHANES data is generally thought to be credible and is used to support many studies of supplement use.

“I think they did a good job of laying out the limitations,” ​Shao told NutraIngredients-USA.

But he took issue with the endpoint of the study.  Supplements, after all, can’t claim to treat or prevent disease, nor can they, of course, claim to prevent death.

“I don’t know many products, whether supplements or not, that are meant to lower the risk of death from all causes. That’s a tall order,”​ he said.

Shao also noted that the study design points out a difficulty in looking at the effects of supplements.  Whether someone dies or not, and the age at which they die, are easily captured data points.  What’s harder to measure is whether supplement use was associated with important health benefits in the meantime. You might, or might not, live longer with regular supplement use.  But might you be healthier during that time?

“We know from surveys that consumers don’t use supplements to prevent death.  We know they don’t use them to prevent chronic disease.  Consumers are using these products to fill in nutrient gaps and to promote overall health,”​ he said.

“I’ve never seen a researcher say they have a way to measure health promotion,”​ Shao said.

‘Fake science’

Dan Fabricant, PhD, president and excutive director of the Natural Products Association, was not as deferential to the study’s approach as was Shao.

“I like the term ‘fake science,’”​ he said. “How can you piece out the confounders? You already have a compromised group of people.”​

Farbricant said there are valid ways of discovering the effects of supplements using these large population data sets. Looking at whether the combination of calcium and Vitamin D can prevent fractures in older people is one example, he said.

“I don’t know of anything that is going to extend life. I think that there are so many confounders here that you have to treat this data with a ton of salt. It’s not like they were in a clinic watching what they ate and knowing what they took in. Overall I think it’s laughable,”​ Fabricant said.

Source:​ Annals of Internal Medicine​​​
Association Among Dietary Supplement Use, Nutrient Intake, and Mortality Among U.S. Adults: A Cohort Study​
DOI: 10.7326/M18-2478
Authors: Chen F, Du M, Blumberg JB, et al.