Multivitamin supplements were first made available in the 1940s, and since it's conception, it has grown into a multi-billion dollar industry. People spend over $5 billion US per year on purchasing multivitamins in the United Sates alone and in Australia, it's estimated that over 19% of the population take some kind of multivitamin supplementation, shelling out around half a billion dollars per year. Many people are firm believers in taking multivitamins, claiming that they are the magical bullet, or a long term health insurance policy to help you live longer and healthier; on the other hand, I have seen people, including health professionals blatantly dismiss any potential benefits of multivitamins, claiming that "it doesn't work". So do multivitamins work? By "work" if you mean whether the multivitamins from a pill can get into your body after ingestion then the answer is a big YES. Will your body benefit from taking vitamins on top of your meals, well that depends. In this article, we will explore the truths and myths of multivitamin supplements, we will look at whether taking multivitamins can improve your daily nutritional intake, whether they can prevent diseases, improve sports performance, are they really safe for general consumption, and who should or should not take them. So here is what the latest research has to say.
Multivitamin supplements and daily nutritional intake
Many take multivitamin supplements because they believe that they can help them to achieve the recommended levels of daily nutritional intake, which could not be met by eating food alone. It's like a nutritional insurance policy. While it is true that using multivitamin supplements can improve a person's nutritional intake, it is also a double-edged sword. Depending on the content and the composition of the particular multivitamin product, and the diet of the consumer, it also increases the likelihood of consuming too much of nutrients, to above the upper level of intake (the highest average daily intake level without adverse effects), which in turn, can cause health complications.
A study investigating the effects of taking multivitamin supplements in the US found that, multivitamin supplementation can increase the prevalence of nutritional adequacy in both men and women. The greatest improvements in intake were vitamin E, zinc and vitamin A. However, taking multivitamins also increased the prevalence of excess nutritional intake for vitamin A, iron, zinc and niacin (Murphy et al. 2007, American Journal of Clinical Nutrition). The researchers concluded that multivitamins should be formulated better in accordance with specific demography of people in order to address nutritional inadequacy associated with a particular diet and reduce the chance of excessive dosing.
It has been shown that excessive nutrient intakes are more commonly associated with multivitamin users in comparison to those who take single vitamin supplements (Rock 2007, American Journal of Clinical Nutrition). That is not really surprising as each person is different, with a different nutritional requirement, whereas multivitamin supplements are usually one size fits all. Even with the specialized formulas, such as those made specifically for women or elderlies, they are still not personalized enough to take into account your normal diet, age, weight and height. It also seems like the younger we are, the easier it is for us to exceed the tolerable upper intake limit from multivitamins. Studies showed that over half of the multivitamin users below the age of 13 exceeded the upper intake limit for folic acid whereas approximately 5% of the multivitamin users over the age of 50 exceeded their limit (National Institute of Health 2013).
Effects of taking excessive amount of vitamins and minerals
I'm sure you've heard of the saying "you cannot overdose on vitamins as the body will get rid of the excess through urine". Well that is only partially true. It is correct that most water-soluble vitamins are not stored in the body but that doesn't mean you can assume excess intake is safe. In addition, excess amount of certain water-soluble vitamins can be quite harmful. Excess intake (above the upper level of intake of 2000mg/day) of vitamin C, an antioxidant for example, can have oxidative effect to make it a pro-oxidant; moreover, excess intake of vitamin C can cause oxalate crystalisation, which can lead to kidney stones (Worblewski 2005, Polskie Towarzystwo Lekarskie). Another example is massive and prolonged ingestion of vitamin B6 at 10 grams a day for 5 years can cause sensory and motor neuropathy (nerve disorders) (Morra et al 1993, Functional Neurology). These are just examples of what prolonged, excess intake of vitamins can do, so just remember, even with the water soluble can be harmful at excess levels, don't over dose.
Now let's have a look at fat soluble vitamins, vitamins A, D, E and K. Unlike water-soluble vitamins, fat-soluble vitamins dissolve in fat and stored in the body and can accumulate to dangerous levels over time. Vitamin toxicity can occur from long-term excessive over intake of fat-soluble vitamins, which can have dangerous health complications. However, due to the relatively "moderate" content of over the counter multivitamins, vitamin toxicity is unlikely to occur from normal consumption, unless of course, you decided to abuse it. The level of vitamin A has been shown to be among the most improved following multivitamin intake, which caused percentage of people exceed the upper level of intake. Excessive intake of vitamin A during pregnancy has been shown to increase the chance of birth defects (Institute of Medicine 2001). The consequences of excessive intake of fat-soluble vitamins can be quite serious and be potentially life threatening.
Many multivitamin supplements also contain minerals, such as iron, calcium, zinc and copper. While the minerals are certainly essential for the function of the body, excess intake can also cause serious health complications. Excess iron can cause liver damage (Swanson CA 2003, Alcohol); excess copper can cause neuronal toxicity (Brewer 2012, Biofactors) and excess zinc, even at a level close to the upper limit of the upper level of intake can interfere with the utilization of copper and iron and adverse affect HDL cholesterol concentrations (Fosmire 1990, American Journal of Clinical Nutrition).
So the message I'm trying to get across is that, all vitamins and minerals are essential for the function of the body, the supplementation of these nutrients is okay if you knew that you are not getting enough from the food or being diagnosed with deficiencies. However, make sure to read the content of the supplement packaging and chose a product that contains nothing at a concentration close or higher to the recommended dietary intake or adequate intake values. Pay special attention to the vitamin A and iron content, as most people get enough of them already from food, they are the easy ones to overdose.
Can take multivitamins help to prevent diseases?
That is a tricky question. If you have some form of deficiency then the answer is probably yes. If you are already getting enough nutrients from your normal diet, then as we discussed above, excess intake doesn't really do your body any good. Two randomized trials investigated the disease-prevention effect of multivitamin supplements in over 300,000 women aged between 45-79 over an 8-11 year period found multivitamin supplementation does not reduce the chance of chronic diseases, cancer and mortality (Neuhouser et al. 2009, Archives of Internal Medicine; Park et al. 2011, American Journal of Epidermiology).
On the other hand, independent studies have yielded completely contradictory results. Studies found multivitamin supplementation may increase the chance of breast cancer in Swedish women but have a reduced chance of heart attack. On the contrary, an American study showed the use of multivitamin supplements can in fact reduce the chance of breast cancer in women, however, taking HIGH LEVELS of multivitamins long term may increase the chance of prostate cancer in men (National Institute of Health 2013). The use of multivitamins has also been shown to reduce blood pressure in over-weight Chinese women (Wang et al. 2009, Asia Pacific Journal of Clinical Nutrition).
It is difficult to obtain accurate data from small independent studies, as there are just way too many variables at play that could skew the results. Results from randomized trials are said to be relatively more accurate, however, not many trials have been conducted to study the effects of multivitamin supplements. A trial investigated whether multivitamin supplementation can prevent chronic disease in men aged over 50 over an 11.2 year period and found multivitamin supplementation did not reduce the risk of chronic diseases, however, it did reduce the risk of cancer by 8% (Gaziano et al. 2012, JAMA).
Other randomized trials have also concluded that the use of multivitamin supplementation can significantly reduce the chance of cancer and all-cause mortality in men but not women. Moreover, it can significantly reduce age related eye diseases in both men and women. Other trials have found multivitamin supplementation can reduce fasting blood glucose levels, however, it does not reduce the risk of diabetes in 50-71 year old adults (National Institute of Health 2013). The supplementation of folic acid containing multivitamins can significantly reduce the occurrence and recurrence of neuron tube defects (Czeizel AE 2011, Annals of Nutrition and Metabolism).
Experts in the field have concluded that there are realty no concrete evidence support nor against the use of multivitamins (Due to contradictory results). But they won't recommend it anyway due to the possible safety concerns. People with a healthier lifestyle tend to take more multivitamins, and because everyone's diet is different, plus there are so many different varieties of multivitamins available, it is difficult to standardize the studies and trials. Moreover, the parameters and time frames used by each study/trial is limited, thus the full effect of multivitamin supplementation cannot be investigated. Due to the above factors, no study can really make a cause-effect claim regarding to multivitamins.
Multivitamins are not medicines, they merely provide nutrients that we should obtain enough from food, drinks and our surrounding environments. Too much or too little nutrients will affect the optimal function of the body, thus gulping down the vitamin pills will not make you more super human than your body's own natural capabilities under optimal conditions. Do not believe the over-hypes surrounding multivitamin supplements, yes they will probably make you feel and function better if you are not getting enough nutrients from the food you eat. However, if your nutritional status is adequate, multivitamin supplements will not make it "more adequate", instead, you will just run a higher chance of overdosing yourself, which can be potentially harmful.
Multivitamins and sport performance
Can taking multivitamins improve sports performance? Well, it's has been establish that deficiency in vitamin C can reduce aerobic power but does not decrease endurance capability. Supplementation of multivitamins to athletics with a normal vitamin balance does not improve their performance (American Dietetic Association et al. 2009, Medicine and Science in Sports and Exercise). The supplementation of antioxidants did not reduce exercise induced oxidative stress (Ferrer et al. 2009, International Journal of Sports Nutrition and Exercise Metabolism). However, athletic with known deficiencies or on a poor diet can use supplements to improve their nutritional status, which will in turn help with performance and recovery.
So is it safe to take multivitamins?
We just spent paragraphs discussing the pros and cons of multivitamins. One may ask, if there are so many bad effects of excessive intake of vitamins and minerals, is it still safe to take them? To answer this question, I will need to first clarify that most studies and trials were conducted under very specific conditions on a very specific groups of subjects. Some studies used ultra-high dose of multivitamins most of us don't get exposed to. To us average people, the current recommendation by the National Institute of Health of America is that taking basic multivitamins that provides approximating recommended intakes should pose no safety risks to healthy people. However, if you are taking additional nutritional supplements, or fortified foods (with extra vitamins/minerals such as vitamin water), then you will run a higher risk of excess intake of certain nutrients at level above the upper level of intake, which consequently increases the possibility of adverse effects.
Who should or shouldn't take vitamin supplements?
Basic over the counter multivitamins should be safe for the consumption of healthy people. If you are on a special diet and/or do not eat balanced meals on a regular basis, then multivitamin supplementation might be beneficial. In addition, components of multivitamin supplements can be beneficial to certain population groups. The most obvious one would be people with vitamin and/or mineral deficiencies. Based on the results of some of the studies investigating effects of multivitamin supplements, around 25% of the subjects tested had some sort of nutritional deficiency in America (Murphy et al. 2007, American Journal of Clinical Nutrition). In Australia, it was suggested that over 1/3 of the adult population have vitamin D deficiency, and over 73% of adults have vitamin D levels that are considered below the optimal for musculoskeletal health, which is a key factor for falls and fractures in the elderly (Daly et al. 2012, Clinical Endocrinology). Vitamin supplementation in these people may be beneficial. However, it is unlikely for a person to be deficient to all vitamins and minerals and thus taking multivitamins might be a bit of overkill. Supplementation of a single vitamin/mineral is sufficient.
It was suggested that supplementation of vitamin D and calcium in post-menopausal women can increase bone mineral density and prevent fracture; supplementation of synthetic folic acid (400mg/day) can reduce the chance of neural tube defects in newborns; vegans and people over the age of 50 are recommended to take vitamin B12 supplements as they are less able or like to absorb it from food; it's recommended that breastfed or partially breastfed infants should receive 400IU/day vitamin D shortly after birth until they are weaned; similarly, vitamin D supplementation is also recommended for non-breastfed infants if they drink less than 1000mL/day of vitamin D fortified formula. Please consult a healthcare professional if you think you belong to one of the groups of people above and want to take nutritional supplements.
Who shouldn't take vitamin supplements?
One man's best friend is another man's poison. This phrase is so very true here. There are particular groups of people who should really pay extra attention on what's in your supplements, as taking the wrong thing can really have detrimental effects on your health.
- Smokers, ex-smokers and asbestos exposed persons: beware of vitamin A and beta-carotene! Smokers took supplements that contain beta-carotene (20mg/day, maximum recommended dietary intake is 6mg/day) had an 18% higher chance of lung cancer after 5-8 years (New England Journal of Medicine 1994). Smokers, ex-smokers and asbestos exposed persons who took 30mg/day of beta-carotene and 25,000IU/day of vitamin A (recommended dietary intake 2300-3000IU) had a 28% higher chance of getting lung cancer (Omenn et al. 1996, New England Journal of Medicine).
- Pregnant women: excess amount of vitamin A intake can increase the chance of birth defects in infants.
- Adult male, post-menopausal women and children under of age of 6: should avoid taking multivitamins containing the adequate intake level of iron unless you are being diagnosed with iron deficiency or inadequacy in order to avoid iron poisoning.
- People who are on anti-blood clotting medications: please consult your healthcare professional before taking any supplements containing vitamin K, as vitamin K is involved in blood clotting and would reduce the efficacy of your medications.
How should I choose multivitamin supplements?
Ideally, it would be nice to know your nutritional status before choosing a multivitamin product. The most common method for testing nutritional status is through blood tests, sounds simple but it is also insensitive and inaccurate for many nutrients. The reason for that is nutrients are usually stored at specific sites in the body and on the other hand, blood samples are usually not representative of the sites. You could have normal blood tests results even if you are deficient (such as zinc), or a mildly abnormal result that doesn't actually mean much clinically (such as vitamin B6). To obtain more accurate results, tests have been developed to measure nutrient at the sites they act. However, it is cost and time consuming for a normal healthy person to do these tests just for the purpose of choosing multivitamins.
The following recommendations may be helpful as a general rule of thumb for multivitamin shopping. Remember, if you suspect that you are sick, always consult a healthcare profession before drugging yourself up. For general multivitamin shopping, one should always choose a product that's specifically made for your gender, age and special requirements (ie. pregnancy or post-menopausal). Avoid high levels of vitamin A and beta-carotene if you are smoker or ex-smoker. Men should also choose multivitamins contain little or no iron. Do not use products that contain nutrients exceed their recommended dietary intake values.
The human body is extremely complex, vitamins and minerals, albeit essential, are only a small part of our building blocks. Multivitamins may be helpful in maintaining the optimal levels of nutrients in the human body, but it is by no means a replacement for your normal diet. Excess intake of nutrients from supplements can be more harmful to your body than not taking any supplements at all. In a world of fast foods, many do consume insufficient nutrient-dense foods and beverages. Vitamin supplements may have its place in the current society. But remember, nothing beats a good balanced meal and a healthy lifestyle.