Millions of people take multivitamin pills daily in order to benefit from the health and protective benefits they purportedly provide. Multivitamins are among the most popular health supplements used today, with surveys revealing that billions of dollars are spent on these products each year. Many people also take multivitamins to either maintain their health and fitness, or to avoid chronic diseases.
Obtaining all necessary vitamins and elements required by the body through downing a multivitamin pill each day is certainly an appealing prospect. However, mounting evidence shows that intake of daily multivitamins may not provide users with any real protective health benefits, in particular when it comes to chronic conditions such as heart disease and cancer. Moreover, in the case of healthy individuals, multivitamins have been proven to provide no added protective benefits to their body, while increasing risk of negative outcomes.
The new observational study by researchers at the National Cancer Institute in the United States involved around 400,000 adults, without a history of chronic diseases, over a follow-up period of more than 20 years. Those taking a daily multivitamin showed no improvement in mortality risk compared to those who did not.
On the contrary, those who were taking the supplement demonstrated a slightly increased (4%) mortality risk.
The study was initiated to augment the limited data currently available to categorically ascertain the benefits and harms from the daily use of multivitamins. The researchers leveraged data from three large and geographically diverse US cohort studies on 390,124 healthy adults with follow-up data spanning a 20-year time period. The study aimed to evaluate the association between the daily use of multivitamins (MV) and mortality outcomes from chronic diseases.
The study’s size and length are two of its greatest strengths. However, it is observational in nature, meaning that, unlike a controlled trial, it does not demonstrate causality between two events — in this case, taking a multivitamin and death. Instead, it helps to form a picture of any associations between these events at a large scale in the real world.
Part of the difficulty of conducting a study of this nature is the sheer volume of data to sort through and the potential for confounding. The study also had to filter data based on the ‘sick user effect’ and the ‘healthy user effect’, so as to avoid discrepancies in the health outcomes related to MV use. .
The ‘sick user effect’ refers to the possibility that individuals who are sick may more frequently use multivitamins due to their health condition. On the other hand, the ‘healthy user effect’ is the opposite, with individuals who already live a healthy lifestyle being more inclined to use a multivitamin as part of their routine than those who are less health conscious. Without proper controls in place, these effects could lead a researcher to two opposing conclusions about the effects of multivitamins on mortality risk.
The researchers were able to control for these distinct effects, by adjusting for lifestyle factors like smoking, diet, and physical activity. They also excluded individuals with major chronic diseases, including cancer, at baseline to account for the ‘sick user effect’. After controlling for all these factors, they found that those taking a multivitamin did not have a lower risk of all-cause mortality than those who did not. Nor did they observe any benefits related to specific health outcomes, including cancer, heart disease, and stroke.
The findings are in line with prior research, including recommendations made by the US Preventive Services Task Force in 2014 and in 2022, which said there was little to no benefit in taking them. However, the researchers cautioned that findings from their study were not applicable to people using dietary supplements to address specific vitamin deficiencies. In particular, this did not apply to people who were taking supplements due to anemia, diabetes, or women who were taking them for postmenopausal conditions, on the recommendations of their doctors or other healthcare professionals.
Doctors opined that the findings were not surprising, as the patients observed were all healthy, without any chronic medical conditions. They added that generally, if you are a healthy individual, and you are exercising, eating a regular diet, consuming adequate fruits and vegetables, you are already getting your regular intake of vitamins and supplements. They added that in such cases, the use of MVs were largely superfluous to overall health.
The need to take a MV is based on many factors, including the patient’s current health, dietary pattern, other supplements being taken, and personal health goals. Generally, MVs should be recommended only if a person is not meeting their nutrient needs, or has an inadequate diet at baseline due to poor appetite, or is not able to meet everything via diet alone. They cautioned that the use of MVs daily was not an insurance against an unhealthy dietary pattern, and should not be taken to cover unhealthy choices of foods that are not nutritionally dense.
