Nutritious foods but not dietary supplements linked to lower mortality risk

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SupplementsAdequate intake of certain nutrients is associated with a reduction in all-cause mortality when the nutrient source is foods, but not supplements, according to a study. There was no association between dietary supplement use and a lower risk of death. In addition, excess calcium intake was linked to an increased risk of cancer death, which the researchers found was associated with supplemental doses of calcium exceeding 1,000 mg/day.

“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 Dr Fang Fang Zhang, 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 a nationally representative sample comprising 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 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.”

The study used 24-hour diet recall data from six two-year cycles of the National Health and Nutrition Examination Survey, through 2010. For each nutrient, the daily supplement dose was calculated by combining the frequency with the product information for ingredient, amount of ingredient per serving, and ingredient unit. Dietary intake of nutrients from foods was assessed using 24-hour dietary recalls. Mortality outcomes were obtained for each participant through linkage to the National Death Index through 31 December, 2011, using a probabilistic match.

The authors note some limitations, including the duration of dietary supplement use studied. In addition, prevalence and dosage of dietary supplement use was self-reported and so is subject to recall bias. Residual confounding may play a role in the observed associations.

First author of this study is Fan Chen, who conducted this work when she was a student at the Friedman School and Tufts University School of Medicine. Additional authors on this study are Mengxi Du, Jeffrey B Blumberg and Luxian Zeng, Guangdong Second Provincial General Hospital; Kenneth Kwan Ho Chui, Tufts School of Medicine; Mengyuan Ruan, Tufts School of Medicine; Gail Rogers, Jean Mayer USDA Human Nutrition Research Centre on Ageing at Tufts University; and Zhilei Shan, Friedman School and Harvard TH Chan School of Public Health.

Abstract
Background: The health benefits and risks of dietary supplement use are controversial.
Objective: To evaluate the association among dietary supplement use, levels of nutrient intake from foods and supplements, and mortality among U.S. adults.
Design: Prospective cohort study.
Setting: NHANES (National Health and Nutrition Examination Survey) data from 1999 to 2010, linked to National Death Index mortality data.
Participants: 30 899 U.S. adults aged 20 years or older who answered questions on dietary supplement use.
Measurements: Dietary supplement use in the previous 30 days and nutrient intake from foods and supplements. Outcomes included mortality from all causes, cardiovascular disease (CVD), and cancer.
Results: During a median follow-up of 6.1 years, 3613 deaths occurred, including 945 CVD deaths and 805 cancer deaths. Ever-use of dietary supplements was not associated with mortality outcomes. Adequate intake (at or above the Estimated Average Requirement or the Adequate Intake level) of vitamin A, vitamin K, magnesium, zinc, and copper was associated with reduced all-cause or CVD mortality, but the associations were restricted to nutrient intake from foods. Excess intake of calcium was associated with increased risk for cancer death (above vs. at or below the Tolerable Upper Intake Level: multivariable-adjusted rate ratio, 1.62 [95% CI, 1.07 to 2.45]; multivariable-adjusted rate difference, 1.7 [CI, −0.1 to 3.5] deaths per 1000 person-years), and the association seemed to be related to calcium intake from supplements (≥1000 mg/d vs. no use: multivariable-adjusted rate ratio, 1.53 [CI, 1.04 to 2.25]; multivariable-adjusted rate difference, 1.5 [CI, −0.1 to 3.1] deaths per 1000 person-years) rather than foods.
Limitations:
Results from observational data may be affected by residual confounding. Reporting of dietary supplement use is subject to recall bias.
Conclusion: Use of dietary supplements is not associated with mortality benefits among U.S. adults.

Authors
Fan Chen, Mengxi Du, Jeffrey B Blumberg, Kenneth Kwan Ho Chui, Mengyuan Ruan, Gail Rogers, Zhilei Shan, Luxian Zeng, Fang Fang Zhang

Tufts University Health Sciences material
Annals of Internal Medicine abstract


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