Getting the right amount of vitamins and minerals can lower risk of an early death, but they should come from food instead of supplements, suggests a new study by US researchers. The team from Tufts University say they found no association between the use of dietary supplements and a lower risk of death.
But the study has been branded “fake science” by the trade association the Natural Products Association, which has accused the researchers of spreading “misleading information”.
“As potential benefits and harms of supplement use continue to be studied, some studies have found associations between excess nutrient intake and adverse outcomes, including increased risk of certain cancers,” said Fang Fang Zhang, M.D., Ph.D., associate professor at the Friedman School of Nutrition Science and Policy at Tufts University and senior and corresponding author on the study. “It is important to understand the role that the nutrient and its source might play in health outcomes, particularly if the effect might not be beneficial.”
The study used data from more than 27,000 US adults ages 20 and older to evaluate the association between dietary supplement use and death from all causes, cardiovascular disease (CVD), and cancer. The researchers assessed whether adequate or excess nutrient intake was associated with death and whether intake from food versus supplement sources had any effect on the associations.
For the association between nutrient intake and the risk of death, the researchers found:
- Adequate intakes of vitamin K and magnesium were associated with a lower risk of death;
- Adequate intakes of vitamin A, vitamin K, and zinc were associated with a lower risk of death from CVD; and
- Excess intake of calcium was associated with higher risk of death from cancer.
When sources of nutrient intake (food vs. supplement) were evaluated, the researchers found:
- The lower risk of death associated with adequate nutrient intakes of vitamin K and magnesium was limited to nutrients from foods, not from supplements;
- The lower risk of death from CVD associated with adequate intakes of vitamin A, vitamin K, and zinc was limited to nutrients from foods, not from supplements; and
- Calcium intake from supplement totals of at least 1,000 mg/day was associated with increased risk of death from cancer but there was no association for calcium intake from foods.
In addition, the researchers say they found that dietary supplements had no effect on the risk of death in individuals with low nutrient intake. Instead, the team found indications that use of vitamin D supplements by individuals with no sign of vitamin D deficiency may be associated with an increased risk of death from all causes including cancer. Further research on this potential connection is needed.
“Our results support the idea that, while supplement use contributes to an increased level of total nutrient intake, there are beneficial associations with nutrients from foods that aren’t seen with supplements,” said Zhang. “This study also confirms the importance of identifying the nutrient source when evaluating mortality outcomes.”
‘Fake science’ allegation
The study came in for sharp criticism this week from the Natural Products Association (NPA), the leading US trade association for the health foods and supplements industry.
The NPA saysthat the study “observed an unhealthy patient population – including cancer survivors and people in generally poor health – to make misleading claims about the health benefits of nutritional supplements.”
Daniel Fabricant, president and CEO of NPA, commented: “This is fake science and it’s spreading misleading information to the general public. The first line of defence against disease is a balanced healthy lifestyle, and supplements are important for the vast majority of Americans who may not receive the recommended daily nutrients from diet alone.”
The NPA asserts that diet in those already diagnosed with cancer in the past was a major confounder in the study. In a statement, it said: “The participants were more likely to be cancer survivors, smokers, physically inactive, diabetic, and in poor general health. The trend toward higher risk of death with an increasing number of supplements was not statistically significant in the sample size of 30,000. Furthermore, the use of vitamin E supplements in combination with multivitamins was associated with lower risk of death.”
The study’s authors acknowledge that their work has “some limitations”, including the duration of dietary supplement use studied. They also noted that the self-reporting methods of charting supplement use was also “subject to recall bias” and that “residual confounding may play a role in the observed association”.