Sometime in 2020, broadcaster and doctor Xand van Tulleken began to question his understanding of health and wellness, despite two decades of medical practice.
His realization stemmed from conversations with friends and colleagues who discussed their microbiome analyses, genetic test results, and data from continuous blood-glucose monitors. He also observed a surge in health and wellness information being discussed on television and radio.
Van Tulleken embarked on an investigation into popular health advice, including questions about NAD supplements, the benefits of continuous glucose monitors for weight loss, red-light therapy, turmeric, microplastic testing, and biological age assessments. His research, which involved poring over scientific evidence with expert colleagues, led him to conclude that “very little” of this advice has proven effective.
Vitamins and Antioxidants Under Scrutiny
Vitamins form the basis of nutrition science, with essential roles in vision, energy production, and immune function. While it is logical to assume that modern diets may not provide optimal vitamin intake, leading to a need for supplements, large-scale research trials have yielded consistent results.
Numerous studies on multivitamin supplementation, including vitamin C, have failed to demonstrate a preventative effect against chronic diseases like cancer and cardiovascular disease, nor have they decreased the risk of premature death. Some research even suggests a potential increase in mortality risk.
A 2007 meta-analysis of 68 randomized trials involving nearly 250,000 participants examined the impact of antioxidant supplements, such as vitamins A, C, E, beta-carotene, and selenium, on mortality. The study concluded that these supplements do not reduce mortality and that Vitamins A, beta-carotene, and vitamin E could increase mortality risk. This study has been cited over 1,500 times. Subsequent analyses, which rigorously removed potential data distortions, indicated an increased mortality risk of up to 16 percent.
Despite this evidence, the public's behavior regarding supplement use often appears at odds with scientific findings. Further large, long-duration trials, including the Women's Health Study and the Heart Protection Study, found no reduction in cancer or cardiovascular disease rates among participants taking antioxidant vitamins. The Physicians' Health Study II found a modest reduction in total cancer incidence but no significant effect on major cardiovascular events.
The COSMOS trial, published in 2022, followed over 21,000 older adults for more than three years, investigating the effects of a daily multivitamin. The trial found no significant reduction in invasive cancer, cardiovascular disease, or all-cause mortality. While sub-analyses explored cognition and biological aging, yielding headlines about potential benefits, the study's authors did not support the use of multivitamins for cancer or cardiovascular disease prevention in generally healthy older individuals. The interpretation of these sub-studies, particularly regarding cognitive decline, has been met with skepticism due to small observed benefits and methodological considerations.
The Complexity of Human Biology
Van Tulleken highlights that the efficacy of a substance in cell cultures or animal models does not guarantee its effectiveness in humans. He uses the analogy of motorways leading into a city to explain the complexity of biological systems. Just as closing one road does not solve traffic congestion because people will find alternative routes, intervening in biological pathways may not yield the expected results due to the body's intricate network of compensatory mechanisms.
Furthermore, what appears as a problem from one perspective (e.g., traffic congestion) can be essential for another aspect of the system (e.g., economic activity). Similarly, biological processes are complex, and simple interventions may not address the root cause or may disrupt beneficial functions.
Vitamin D Hype vs. Reality
By the late 20th and early 21st centuries, observational studies linked low vitamin D levels to numerous health issues, including cancer, diabetes, and heart disease. This led to widespread recommendations for vitamin D supplementation.
However, large-scale randomized controlled trials, such as the VITAL trial involving over 25,000 participants, have largely failed to demonstrate these supposed benefits. Vitamin D supplementation did not prevent cancer or cardiovascular disease, nor did it improve cognitive function or reduce falls. Notably, even in trials involving individuals with osteoporosis, vitamin D supplements did not reduce fracture rates.
While vitamin D supplementation is advised to prevent deficiency diseases like rickets and osteomalacia, particularly for at-risk groups and during winter months, it does not deliver the broader health promises promoted by the wellness industry.
Van Tulleken suggests that while supplements can be useful as prescription drugs to address specific medical conditions, such as iron for anemia or vitamin B12 for vegans, their widespread use for general health improvement is not supported by robust scientific evidence. He concludes that simple solutions offered for complex health problems are unlikely to be effective and encourages a focus on established health practices like improved diet and cognitive engagement.