Taking supplements such as vitamins, minerals, amino acids, and enzymes can boost the body's total nutrient intake. Some common dietary supplements include calcium, vitamin D or fish oil. This can help both with improving fitness and with improving one's diet -- but there's a catch.
Although supplementation is advised in certain situations, such as physical training or recovery following an illness, it can sometimes cause unwanted problems.
Researchers at Tufts University analyzed a dataset involving more than 27,000 American adults in order to assess whether adequate or excess nutrient intake change all-cause mortality, as well as whether anything changed when some of the nutrients came from supplements rather than food.
According to these results, adequate intake of certain nutrients from food -- but not supplements -- was linked to a reduction in all-cause mortality.
There was no association between taking supplements and a lower risk of death. However, excess calcium intake (more than 1,000 mg/day) was linked to an increased risk of death from cancer.
"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, 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."
Some of the key findings concerning the association between nutrient intake from food and risk of death were that:
- 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 cardiovascular disease; and
- Excess intake of calcium was associated with higher risk of death from cancer.
- 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.
What's more, the researchers found that the use of vitamin D supplements by individuals who weren't lacking it was associated with an increased risk of death from all causes, cancer included.
"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."
For each nutrient, the daily supplement dose was calculated by combining the frequency with the product information for each ingredient and the amount of ingredient per serving. Meanwhile, the dietary intake of nutrients from foods was assessed using 24-hour dietary recalls.
According to a 2018 survey from the Council for Responsible Nutrition (CRN), 75% of the US individuals took dietary supplements in 2018, marking a significant increase from 65% in 2009. The most popular supplements are vitamin D and calcium, while the main reason why Americans take dietary supplements is overall health and wellness. These new findings, which were reported in the Annals of Internal Medicine, suggest that there may be a threshold of nutrient intake over which dietary supplementation may prove harmful.
The study didn't find a cause-effect connection but rather a correlation. But even absent a direct connection, these findings suggest that the safest course of action is to source most if not all of your nutrients from food.