A new study has found that using dietary supplements such as calcium and vitamin D do not prolong life expectancy, and may even lead to an increased risk of cancer.
Umpaporn | Shutterstock
The study, which was published on April 9th in Annals of Internal Medicine, used data from the National Health and Nutrition Examination survey from 1999 to 2010, which was linked to mortality data from the National Death Index. The sample comprised data from 30,899 US adults aged 20 years old and above.
Nutrients obtained through the consumption of healthy foods can prolong life expectancy and reduce the risk of premature death. However, extracting such nutrients and consuming them in the form of dietary supplements confers no such benefit, according to the new study.
Understanding the role that nutrients play is ‘important’
Associate professor at the Friedman School of Nutrition Science and Policy at Tufts University and senior and corresponding author on the study Fang Zhang explained the motivation for the study, saying 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.”
Certain supplements were identified to pose specific risks, such as excess calcium being associated with an increased risk of cancer mortality.
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.”
Fang Zang, Co-author
Excess calcium intake in the context of this study was defined as doses exceeding 1,000 mg a day. The study was not only focused on the risk of cancer mortality, but also investigated links between supplement intake and all-cause deaths, including cardiovascular disease (CVD).
The objective of the study was stated to be to “evaluate the association among dietary supplement use, levels of nutrient intake from foods and supplements, and mortality among U.S adults.”
Measurements for the study included data on participants’ use of dietary supplements in the previous 30 days, along with their nutrient intake from food and supplements.
The study recorded 3,613 deaths in the median follow-up period of 6.1 years. These deaths included 945 deaths from cardiovascular disease and 805 deaths from cancer. The study was based on 24-hour diet recall data from six cycles of the National Health and Nutrition Examination Survey lasting two years each, through 2010.
To calculate the daily supplement dose of each nutrient, the frequency and the product information for ingredient, amount of ingredient per serving, and ingredient unit were combined.
Nutrients sourced from foods were monitored with 24-hour dietary recalls. Finally, to calculate mortality outcomes for each study participant, matches were made with the National Death Index through December 31st, 2011.
Vitamin K and magnesium only effective when obtained through food
When comparing nutrient intake from food and supplements, researchers found there was a lower mortality risk when adequate intake of vitamin K and magnesium came from food instead of dietary supplements.
There was also a lower risk of cardiovascular disease (CVD) mortality when adequate intakes of vitamin A, vitamin K, and zinc were sourced from food over dietary supplements.
Additionally, while calcium intake of at least 1,000 mg per day was linked to an increased risk of cancer mortality, no such link was found when calcium was sourced from food.
When considering nutrient intake alone and the associated risk of death, researchers found that adequate intake of vitamin K and magnesium were linked to lower mortality risk, and adequate intake of vitamin A, vitamin K, and zinc were linked to a lower risk of CVD mortality. However, excess calcium was linked to an increase risk of cancer mortality.
Vitamin D shown to increase risk of cancer
In individuals who had low levels of nutrient intake, dietary supplements did not affect their mortality risk. Those taking vitamin D supplements where no vitamin D deficiency was present showed a possible association with an increased risk of all-cause mortality, including cancer. However, this link requires further investigation to be definitively proved as a positive association.
Patient-based answers may have limited the study
Limitations in the study were acknowledged, which included the duration of dietary supplement use studied, as well as the fact that the prevalence and dosage of supplements were self-reported, leaving the study open to recall bias. Additionally, the possibility that residual confounding may have affected the study’s results remains.
Despite this, the researchers concluded:
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. This study also confirms the importance of identifying the nutrient source when evaluating mortality outcomes.”
Association Among Dietary Supplement Use, Nutrient Intake, and Mortality Among U.S. Adults: A Cohort Study. Ann Intern Med. 2019. DOI: 10.7326/M18-2478.