Vitamin supplements can be an effective method to incorporate vitamins that may be missing from our diet. However, they are not a cure-all.
The vitamin and mineral supplement industry is projected to have a value of $32.7 billion (£24.2 billion), with over 74% of Americans and two-thirds of Britons acknowledging their use to enhance their health.
Nevertheless, these supplements are surrounded by debate, with some research indicating that they offer no significant health advantages, while other studies suggest they might even be detrimental. So what does the research actually indicate? Should everyone consider taking vitamin supplements, or is it only necessary for certain individuals? Is there anyone who truly needs to supplement their diet with them?
People consume vitamins and minerals for various reasons.
These compounds are essential for our health, yet our bodies do not produce them naturally. Since we cannot synthesize them, we must obtain them through our diet. For instance, vitamin A is crucial for maintaining good vision and skin health, while vitamin C plays a significant role in supporting the immune system, and vitamin K is important for blood coagulation. Essential minerals such as calcium, magnesium, selenium, and potassium also play vital roles in our health. Vitamins and minerals are categorized as micronutrients because our bodies require them in much smaller quantities compared to macronutrients like carbohydrates, proteins, and fats.
It is important to note that no supplement can truly substitute for a nutritious and balanced diet. Thus, the most effective way to fulfill the body's vitamin needs is by consuming a variety of leafy greens, fruits, grains, nuts, dairy products, and fish. However, studies indicate that many individuals struggle to follow this guideline. The increase in fast food and highly processed options often leads to convenience being prioritized over preparing fresh, home-cooked meals.
"There’s data showing the average American is consuming only half of the recommended fruits and vegetables," remarks Bess Dawson-Hughes, a senior researcher at the US Department of Agriculture's Human Nutrition Research Center on Aging and a professor of medicine at Tufts University. "If you find yourself in that situation, you're likely missing crucial nutrients."
Could multivitamins assist in bridging this nutritional deficit? The response, as you might anticipate, is intricate. The idea that increasing vitamin C intake could prevent the common cold became widespread in the Western world during the 1970s, largely due to influencers like Linus Pauling, a Nobel laureate in chemistry, who asserted that consuming up to 50 times the recommended amount of vitamin C could combat a range of ailments, including influenza, cardiovascular issues, cataracts, and even cancer. While the belief that excessive vitamin C can cure a cold has been thoroughly disproven, many individuals still hold onto this idea.
Fast forward to the present, and social media influencers are endorsing supplements that offer up to 500% or even 1,000% of the recommended daily allowance of vitamins and minerals, despite the reality that dietary supplements are generally unregulated, may contain undisclosed components, and lack support from randomized controlled trials—the benchmark of medical research.
"Mega-dosing" on vitamins and minerals can pose significant risks. For example, there have been cases where individuals required hospitalization due to dangerously elevated levels of vitamin D. Overconsumption of vitamin D can lead to mild symptoms, such as increased thirst and more frequent urination, but in extreme cases, it can result in seizures, coma, and even fatalities.
According to the National Institutes of Health (NIH) in the US, an overload of vitamin A can lead to serious symptoms such as "intense headaches, blurry vision, nausea, dizziness, muscle pain, and coordination issues. In extreme cases, excessive intake of preformed vitamin A can even result in coma or death."
Clinical trials conducted on vitamins and minerals often yield conflicting results, indicating that the potential benefits of vitamin supplements can vary based on individual characteristics and the specific micronutrient contained in the supplement.
The clinical studies conducted on vitamins and minerals
Some of the initial studies concentrated on antioxidants, which are compounds that combat damaging substances known as free radicals. Free radicals are unstable substances that interact with and damage cells and DNA. It may seem logical to assume that increasing antioxidant intake would help prevent disease, but research has consistently shown that this is not the case. For instance, double-blind, placebo-controlled studies led by JoAnn Manson, a professor of epidemiology at the Harvard School of Public Health, discovered that the antioxidants beta-carotene, vitamin C, and vitamin E did not prevent cancer or cardiovascular conditions.
Moreover, some research indicates that taking high doses of antioxidants can potentially be harmful to one’s health. For example, evidence is accumulating from randomized clinical trials suggesting that consuming large amounts of beta-carotene supplements may elevate the risk of lung cancer, particularly among smokers. Additionally, a study by Manson indicated that excessive intake of vitamin E is associated with a higher risk of haemorrhagic stroke.
"Vitamin E acts as a blood thinner, meaning that consuming it in large amounts can reduce the blood's ability to clot, thus increasing the likelihood of brain bleeding," Manson explains.
"Moreover, there is a possibility that extremely high doses of antioxidants might have the opposite effect and actually promote oxidation instead."
Consuming very large amounts of a single micronutrient can also affect the body's ability to absorb other similar micronutrients. For instance, excessive intake of beta-carotene is believed to be detrimental because it can hinder the absorption of other carotenoids, like lutein, which is present in leafy greens such as spinach and kale.
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The importance of vitamin D
Exceeding the recommended daily intake of antioxidants is discouraged. However, what about other vitamins? A nutrient that many individuals lack sufficient levels of is vitamin D, a compound crucial for the development and upkeep of strong bones. Technically, vitamin D is not a vitamin because our bodies can produce enough of it as long as our skin is exposed to adequate sunlight. We can also obtain it from some dietary sources.
Since sunlight exposure is limited during the winter months, UK public health guidelines recommend that everyone should take vitamin D supplements from October to March. In fact, there is a suggestion that anyone residing north of 37 degrees latitude, comparable to Santa Cruz in the US, should consider taking a vitamin D supplement during the winter season. This also applies to individuals living more than 37 degrees south of the equator.
Why vitamin D matters
Exceeding the recommended daily intake of antioxidants is discouraged. However, what about other vitamins? One nutrient that many individuals lack is vitamin D, a crucial substance for developing and preserving healthy bones. Vitamin D is not classified strictly as a vitamin, since our bodies can produce enough of it as long as our skin is exposed to sufficient sunlight. In addition, we can obtain it from specific foods.
Due to the limited sunlight during winter months, the public health advice in the UK is for everyone to take vitamin D supplements from October to March. There is even a viewpoint that anyone residing north of 37 degrees latitude, which is around the location of Santa Cruz in the US, should consider supplementing with vitamin D during the winter. This recommendation also extends to individuals living more than 37 degrees south of the equator.
Due to limited sunlight during the winter, public health guidelines in the UK advise that everyone should take vitamin D supplements from October to March. There’s a case to be made that anyone residing north of 37 degrees latitude—similar to the US city of Santa Cruz—should consider a vitamin D supplement during the winter months. This recommendation also extends to individuals living more than 37 degrees south of the equator.
One of the significant studies on vitamin D was Manson's Vital trial, which included more than 25,000 adults from the US. The trial examined whether daily supplementation of vitamin D or omega-3 fatty acids could lower the risk of developing cancer, heart disease, and stroke in individuals with no previous history of these conditions.
Although vitamin D supplements did not influence the overall incidence of cardiovascular disease, strokes, or cancer, there was a 17% decrease in cancer-related deaths among those who took vitamin D. When Manson specifically analyzed participants who had been taking vitamin D for two years or longer, there was a statistically significant 25% reduction in cancer deaths, along with a 17% decrease in cases of advanced metastatic cancer.
"It is possible that vitamin D influences the biology of tumor cells, making them less aggressive and reducing their likelihood of metastasizing, but it does not impact the initial diagnosis of cancer," Manson explains.
The Vital trial has revealed that vitamin D supplements notably decrease the incidence of autoimmune disorders like rheumatoid arthritis and psoriasis.
Because vitamin D is essential for sustaining strong bones, it has often been suggested that daily vitamin D supplements could help avert bone fractures, especially among older adults. A clinical trial conducted in France in the early 2000s indicated that elderly individuals, particularly women living in care facilities, might experience advantages from vitamin D supplementation.
Nevertheless, following research has produced inconsistent results. The Vital trial demonstrated that vitamin D did not reduce the occurrence of bone fractures, while two additional studies, the Vida study and the D-Health study, also revealed no significant advantages of vitamin D supplementation concerning fractures or falls. However, Dawson-Hughes suggested that the trial participants might not have experienced benefits because they already possessed sufficient levels of vitamin D.
"None of the trials included older adults with low vitamin D levels as a requirement for participation, and they occurred during a period when vitamin D was being promoted as a remedy for various ailments, which led to a surge in vitamin D sales in the United States," states Dawson-Hughes.
"Consequently, the baseline vitamin D levels of the majority of participants were already within the preferred or optimal range."
When is it advisable to take a multivitamin?
Interestingly, emerging evidence suggests that taking a daily multivitamin may be advantageous for health, especially among older adults.
The Physician’s Health Study II, led by Manson, which commenced more than two decades ago, revealed that the likelihood of being diagnosed with cancer was reduced by 8% in individuals who took a daily multivitamin for 11 years. The most significant benefit was observed in participants over 70 years old, who experienced an 18% decrease in cancer risk compared to those who received a placebo.
"Might be because older individuals tend to have a somewhat less nutritious diet," explains Manson. "Or it could be due to difficulties in absorbing vitamins and minerals, which means this demographic may gain more from supplementation."
Additionally, in Manson's 2023 Cosmos trial, those taking daily multivitamins showed a 60% reduction in cognitive decline over three years when compared to the placebo group. Multivitamins have also been associated with a decreased incidence of cataracts.
"These conditions are all associated with aging – such as cancer, cataracts, and memory loss related to cognition – and randomized trials have linked multivitamins to a reduction in all three," states Manson.
So, how does this inform us on the question of who ought to take vitamins? Both Manson and Dawson Hughes suggest that for most individuals, a vitamin supplement is unnecessary, and it is preferable to obtain the nutrients you require from a nutritious, balanced diet. Nutrients from food are absorbed by the body more effectively, and you also gain other beneficial components found in foods, like fiber, which is crucial for digestive health.
While vitamins and minerals are vital for well-being, only minuscule quantities are required for proper functioning, and research clearly indicates that exceeding these amounts offers no additional benefits. Nevertheless, it is evident that some individuals might find a multivitamin pill advantageous, provided that the vitamin concentrations do not surpass the recommended daily intake.
The NHS in the UK recommends that pregnant individuals should take multivitamins and folic acid, which has been shown to effectively reduce the risk of neural tube defects in developing fetuses.
There is strong evidence suggesting that vegetarians or those who consume little fish could gain from taking omega-3 fish oil supplements. The Vital study indicated that participants with low fish intake who were given omega-3 fish oils experienced a 19% decrease in major cardiovascular incidents compared to those given a placebo. Conversely, individuals who ate more than one-and-a-half servings of fish weekly did not see similar benefits. Certain conditions, like Crohn's disease and ulcerative colitis, can hinder vitamin absorption, making supplementation beneficial for affected individuals. Additionally, some medications, such as metformin—which is prescribed for type 2 diabetes—can also impact how the body absorbs vitamins.
It is suggested that adults aged 60 or older might benefit from taking a daily multivitamin to lower their cancer risk and slow cognitive decline, although more research is needed in this area.
Lastly, older adults, particularly those residing in nursing homes—who often have limited diets and do not spend much time outdoors—could benefit from taking combined vitamin D and calcium supplements to help prevent osteoporosis and bone fractures.
"The extensive French research conducted among nursing home residents indicated that merely substituting those two nutrients led to a 40% decrease in hip fractures," explains Dawson-Hughes.
"I believe we need to revisit that evidence to determine if adults living in the community could benefit, or if other individuals who lack calcium and vitamin D could gain from it. This is crucial information we need because a significant portion of the global population suffers from deficiencies in both."
Lastly, Manson emphasizes that "mega-dosing," or consuming vitamin quantities exceeding the recommended daily intake, is not advisable.
"It truly is the case that higher amounts are not always better," she notes.
"However, multivitamins are very safe, so if anyone is worried about not receiving a sufficiently nutritious and balanced diet, taking a multivitamin might provide some assurance that they are obtaining these essential vitamins and minerals."
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