Peer Reviewed

Review Article

Vitamin and Mineral Shortfalls: Frequently Asked Questions About Closing Dietary Gaps

Angelo Tremblay, PhD, and Pamela R. Kushner, MD

ABSTRACT: Large-scale dietary intake surveys from North America have shown that many vitamins and essential minerals are underconsumed by the general population relative to recommended levels. People with certain medical conditions such as diabetes, obesity, and inflammatory bowel disease are at increased risk for these and other micronutrient shortfalls. Older adults, persons in socioeconomically disadvantaged populations, and persons taking certain medications have increased or otherwise unique nutritional needs that require clinical consideration. Lifestyle choices and behaviors such as alcohol abuse and adherence to certain diets (eg, vegan, vegetarian, gluten-free) also can increase the risk for dietary gaps. Dietary supplementation might be necessary for some patients to ensure adequate intake of vitamins and minerals. A daily multivitamin along with dietary counseling is a practical and effective strategy to address dietary gaps in at-risk populations.

KEYWORDS: Vitamins, minerals, micronutrients, dietary gaps, dietary supplements, multivitamins, dietary counseling

Recent nutritional surveys in the United States and Canada have shown that many North Americans are not consuming the recommended levels of many micronutrients from dietary intake alone.1,2 These nutritional gaps are pervasive, and large segments of the population are at increased risk for inadequate micronutrient intake and even deficiency. In this article, we review common questions from a clinician’s perspective on how to address nutritional shortfalls in clinical practice, including the role of multivitamins and mineral supplementation, and provide evidence-based answers and practical guidance.

Frequently Asked Questions

What proportion of people in the United States and Canada have inadequate micronutrient intake? Which micronutrients are of particular concern?

“What We Eat in America,” the dietary component of the National Center for Health Statistics’ National Health and Nutrition Examination Survey (NHANES) report for 2007-2010, showed that a large majority of Americans have an inadequate intake of certain micronutrients from dietary sources alone.1 Despite a population that is increasingly obese, dietary gaps occur because much of the food eaten generally is not nutrient-dense. For example, the intake of vitamins D and E was below the estimated average requirement (EAR) in 94% and 88% of Americans, respectively.1 In addition, one-third to one-half of Americans had an inadequate intake of magnesium, calcium, and vitamins A and C. The 2015 Dietary Guidelines Advisory Committee has stated that vitamins A, D, E, C, as well as folate, calcium, magnesium, fiber, and potassium, are nutrients of concern.1 Iron also is a nutrient of concern for adolescent girls and premenopausal women. Note, however, that interpretation of such data has limitations because it relies on patient self-reports of food consumption.3

The results of similar surveys in Canada have likewise found inadequate intake of magnesium, calcium, and vitamins A and D. Recent data have shown that more than 90% of adults consumed an inadequate amount of vitamin D, and 80% of adults aged 51 years and older had inadequate calcium intake.2


What disease states, conditions, and medications predispose people to nutritional gaps?

People with diabetes are at high risk for inadequate intake of micronutrients, as well as for insufficient levels of circulating micronutrients. A common example of this is hypomagnesemia, which has been shown to increase the risk of cardiovascular disease, diabetic retinopathy, and other complications of diabetes. Population data suggest that 14% to 48% of people with type 2 diabetes have low magnesium levels compared with only 3% to 15% of individuals without diabetes.4

People who have Crohn disease and ulcerative colitis are more prone to inadequate levels of some key micronutrients, such as vitamin D and other fat-soluble vitamins, due to poor absorption.5,6 Vitamin B12 is of particular concern, and supplementation is recommended for individuals with disease in the ileum.6

Homocysteinemia, an established marker of cardiovascular disease, is linked to a lack of folate and some B vitamins.7 Health professionals must consider insufficient vitamin and mineral intake as a potential source of significant clinical problems and that the status of these micronutrients should be monitored to make sure patients progress toward an optimal health status.

Clinicians need to be mindful that magnesium status may not be adequately reflected by serum magnesium levels, because the body takes what it needs from bone and tissues in order to keep serum levels stable.8 The only way to determine magnesium status definitively would be intracellular measurement of magnesium, which is not routinely used in practice. Many clinicians are unaware of the increased incidence of vitamin B12 deficiency among metformin users in the diabetic population, 16% of whom have a borderline deficiency.9

Persons who abuse alcohol often get the majority of their calories from alcohol, resulting in micronutrient deficiencies. Thiamine, folate, vitamin B6, and vitamin B12 deficiencies are a recognized part of the pathogenesis of alcoholic liver disease10,11 and can present particularly in cases of acute alcohol withdrawal.10 Vitamin D has been associated with reduced levels of inflammatory markers in a number of studies. As such, a possible role exists for supplementation in managing multiple chronic diseases, including asthma, atherosclerosis, inflammatory bowel disease, rheumatoid arthritis, and multiple sclerosis.12

Clinicians must recognize that many pharmacologic agents have the potential to interact with micronutrients by blocking absorption or affecting the metabolism of or the excretion of nutrients. Adverse effects of cancer chemotherapy, such as anorexia, stomatitis, and diarrhea, can cause nutrient deficiencies, and antimetabolite chemotherapy can inhibit the synthesis of essential vitamins.13 Many other commonly used medications, including antibiotics, corticosteroids, hormonal agents, proton-pump inhibitors, laxatives, and diuretics, as well as vitamins themselves, can interact with micronutrients, causing altered nutritional status.14 For example, antibiotics such as doxycycline and fluoroquinolones should be taken several hours apart from food, calcium, or other supplements in order to avoid a decrease in micronutrient absorption.


What are special considerations for the increasing prevalence of patients who are obese or overweight, patients who undergo gastric bypass, and patients on special diets?

The best data come from NHANES, which has documented a trend toward an increased prevalence of insufficient intake of some nutrients in individuals who are obese,15 as well as an increase in obesity prevalence over recent decades.16 Inadequate absorption of vitamins A, C, D, and E, and some minerals such as calcium and magnesium, have been found in obese individuals.15 The reasons for this are unclear, although evidence suggests that some vitamins might be sequestered in adipose tissue, reducing their bioavailability.17

Another key area relating to nutrition in obese individuals is gastric bypass and related surgeries, which have the potential to accentuate micronutrient deficiencies.18 Some micronutrients such as copper and iodine, which are absorbed in the stomach, as well as folate and vitamins C, D, K, and B12, which are at least partially absorbed in the ileum, present a significant concern for surgeons performing these procedures. Anemia and osteoporosis also are common in patients who have undergone bariatric surgery.


What nutritional considerations are important for individuals who are following special diets?

The vegetarian/vegan diet particularly can be problematic. People following these diets may not be absorbing sufficient iron and zinc, because vegetarian food sources do not have the same level of bioavailability that animal products have.19,20 Similarly, vitamins A and B12, which are preformed vitamins, are only available naturally from animal-based foods; and vitamin D and calcium are obtained primarily from fortified dairy sources.1,19,20 Vegetarian and vegan diets should be regularly supplemented to prevent deficiencies.

The gluten-free diet is increasingly popular. People with celiac disease tend to have nutritional deficiencies; that being said, many people without celiac disease follow a gluten-free diet because they feel better on it. Because gluten is found in many products that contain wheat, barley, and other grains, these diets often are low in fiber, iron, folate, B vitamins, magnesium, calcium, zinc, and selenium.21,22 People following a gluten-free diet should be advised to consume ample amounts of fruits and vegetables and other nutrient-rich foods such as quinoa and buckwheat.

The Paleolithic or “Paleo” diet is designed to resemble that of our hunter-gatherer ancestors. These diets are characterized by a high intake of vegetables, fruit, and meat; a moderate intake of nuts, berries, and honey; a low intake of grains; and no milk or dairy products, legumes, salt, or refined carbohydrates. Calcium intake can be particularly low with this diet.23 The health claims about these diets do not include the possible long-term effects of a large quantity of meat in the diet.

Low-carbohydrate, high-protein diets also can have nutritional shortfalls. The A TO Z Weight Loss Study24 compared the effectiveness of 4 popular weight-loss diets (Atkins, Zone, LEARN, and Ornish) and found that for the 311 women in the 8-week study, micronutrient intake worsened for all but those following the Zone diet, which led to an improved consumption of vitamins A, C, E, and K. Patients need to be aware of the increased saturated fat and salt and low fiber intake that also could be part of these diets.


What is the role of dietary supplements in overweight and obesity?

Interestingly, the Quebec Family Study25 found that participants who took mineral and vitamin supplements had a lower body weight than those who did not take supplements. This difference was more pronounced in men but also was observed in women. This research team also reported data on supplementation in obese individuals following a healthy eating intervention, with the interesting observation that appetite control was easier in obese women receiving supplementation. This is significant because a weight-reducing program generally leads to progressively increased appetite; ironically, overweight and obese people have an increased risk of vitamin deficiencies and are following or are being put on special diets.

In addition, many obese patients may not mention to their clinician their use of over-the-counter medications that have a weight-loss component given that they may contain stimulants that can cause other problems. It is essential for clinicians to ask about every medication—prescription and over-the-counter—that patients are taking.


What are special considerations for the aging population?

The aging process has a number of effects on nutrient needs and nutrition status. Aging impacts both body composition and how drugs and other substances are metabolized. These include a reduced ability of the kidneys to modify vitamin D, decreased absorption of calcium into bones, loss of muscle mass, increased fat mass, and decreased strength.26 This results in an increased need for various nutrients including protein, calcium, zinc, carotenoids, ω-3 fatty acids, and vitamins C, D, E, and B12.26-28 Often these deficiencies present with general symptoms such as lack of appetite, changes in blood test results, depression, chronic diarrhea, and mouth problems. Aging also can render the body’s immune response less efficient, with inflammatory and antioxidant responses being reduced; the need for vitamin C, vitamin E, and especially zinc may be increased in this population. Indeed, an inadequate store of zinc is a risk factor for pneumonia.28

Inadequate intake of some micronutrients, including vitamins D and B12, has been associated with an increased risk of dementia in the elderly.29,30 Conversely, the increased rate of dementia in elderly patients can make diet alone unreliable as a sole source of nutrients. The majority of adults over the age of 70 do not have adequate intake of calcium and vitamin D from diet alone, which may result in bone loss and an increased risk for osteoporosis.1 An analysis of vitamin D consumption from dietary sources showed that in those 71 years of age and older, 93% of men and 97% of women had a vitamin D intake below the EAR from dietary sources alone.1 Among individuals who used supplements that contained vitamin D, these rates dropped to 7% for men and 13% for women. There also is a potential role for vitamin D in muscle health associated with sarcopenia and muscle weakness in the elderly, which often result in falls.26,31

The efficiency of vitamin B12 absorption decreases with age. The Institute of Medicine estimates that 10% to 30% of adults aged 50 years and older may not be able to absorb adequate amounts of vitamin B12 from normal dietary sources. This population also takes a higher proportion of drugs that reduce B12 levels, such as proton-pump inhibitors. One must also consider vitamin B12 deficiency when neuropsychiatric symptoms such as paresthesias, gait abnormalities, behavioral changes, taste changes, and mouth problems are associated.32 Cognitive decline also can be related to vitamin B12 deficiency.30

A significant decrease in vital eye nutrients such as carotenoids occurs with advancing age. Low macular levels of the nutrients lutein and zeaxanthin are associated with an increased risk of development of age-related eye disease.33,34

Potassium has been deemed a nutrient of public health concern, because low levels of it are associated with cardiovascular diseases and comorbidities. The majority of adults older than 50 years of age do not have an adequate potassium intake, and 3% or less have an intake above the adequate intake level.1 This is exacerbated by medications that can decrease serum potassium levels.14


What other factors put patients at risk for nutritional gaps?

Poverty is an important issue in all populations. NHANES data convincingly demonstrate that when individuals are classified at a low socioeconomic level, they have an increased risk of inadequate micronutrient intake.35 This can be exacerbated when recommended specialty foods or supplements are not accessible to patients who cannot afford them.

A nonpathologic but biologic issue is the case of pregnancy. Pregnancy may be a period of greater risk of inadequacy of some micronutrients, particularly for women who have difficulty eating and comfortably tolerating food during the first months of their pregnancy. Pregnant women are at high risk for vitamin D, calcium, and iron deficiency, so micronutrient supplementation is recommended.36

Smokers are at greater risk for suboptimal nutrient intake and deficiencies such as folate, and vitamins B6, B12, and C.1,37 Of course, the best scenario for these individuals is smoking cessation, but supplementation might be a useful approach to compensate for this addiction.


What is the potential impact of inadequate micronutrient intake on patients’ health?

The optimal nutritional status across different life stages in a healthy population in the United States is generally based on the Recommended Dietary Allowance (RDA) of vitamins and minerals set by the Institute of Medicine.19 Objective markers of nutrition do not necessarily reflect physiologic, physical, cognitive, and emotional function, with many changes in nutritional adequacy occurring at a subclinical level. 

One expert biochemist has theorized that inadequate intake of vitamins and minerals can lead to a triage allocation of available micronutrients.38 This means that if the body gets too little of a vitamin or essential mineral, it will use whatever is available for the most important function that supports short-term survival at the expense of functions that support long-term survival. Ultimately, if there is a nutritional shortfall, this could contribute to the development of chronic disease.

The US Preventive Services Task Force has recommended that clinicians should periodically counsel patients regarding intake of calories, fat, cholesterol, complex carbohydrates, fiber, sodium, calcium, and iron.39 Although most physicians agree with these recommendations,40 they often do not have the necessary time, knowledge, or teaching materials to implement them.41,42

While the importance of nutritional counseling is not questioned, it is difficult to implement in the daily life of a patient,43 particularly as treatment regimens become increasingly complex for patients with multiple comorbidities. The measurement of plasma levels often is not a good measure of micronutrient status.44 Some intracellular testing that can aid in the evaluation of nutritional deficiencies is covered by Medicare.

The role of multivitamins is to improve vitamin and mineral intake in specific populations in a practical way. Data from NHANES demonstrate the efficacy of using dietary supplements in reducing the percentage of the population with inadequate consumption of magnesium, vitamins A, C, and E.45 Other studies across a range of populations have shown that micronutrient deficiencies may be improved by vitamin and mineral supplementation.46-49 That being said, we need to remind patients that multivitamin supplements are not meant to replace healthful diets and lifestyle habits for which there is no other replacement; multivitamins and minerals do not cure disease, and we should advise patients to consult clinicians before taking any high-dose, single-nutrient supplement.

The question is: Is it possible to detect a benefit in the population by observing a significant substantial difference between those using supplementation compared with those not using it? In this regard, a Canadian study was quite convincing.50 Among men and women over 50 years of age, less than 5% who used vitamin supplements had inadequate intake of vitamins A, C, B6, B12, and folate. The same study showed that, in those over 50 years of age, 14% of men and 16% of women who were users of supplements had inadequate intake of vitamin D compared with 74% and 92% of male and female nonusers, respectively. 

These conclusions are supported by the results of the Physicians’ Health Study II,51 the largest study of multivitamins conducted to date, which evaluated male physicians who took either a specific multivitamin (Centrum Silver; Pfizer, New York, New York) or a placebo for 11 years. In this study, multivitamin use was found to be generally safe, with no significant adverse effects, and was associated with an 8% reduced risk of total cancers and a 9% reduced risk of cataracts.51-53 Evidence suggests, therefore, that among supplement consumers there is not only a lower predisposition to micronutrient inadequacy, but also potential benefits regarding the risk of cancer or cataracts.


Is there a risk of excess micronutrient intake in response to multivitamin supplementation?

The safety zone has a tolerance regarding what is considered as excess and a threshold beyond which some symptoms can be detected. NHANES data confirmed that there is little risk of excess micronutrient consumption, demonstrating that the percentage of multivitamin/mineral supplement users with total vitamin/mineral intake greater than the tolerable upper intake level was very low and was zero for some nutrients.3

What do major medical organizations recommend about supplement use?

Many leading medical organizations have made recommendations for the use of supplements (Table). The different groups’ guidelines vary in their recommendations for use of supplementation of various nutrients.


Micronutrient shortfalls are widespread in the general population, even in relatively affluent North America. In addition, large segments of the population, including the elderly, the obese, and those of lower socioeconomic means, are at increased risk for inadequate vitamin and mineral intake, and possibly deficiency. Obtaining the recommended amount of each of the necessary nutrients from food alone may be difficult, even for those dedicated to a healthy and balanced diet. Micronutrient supplementation can be beneficial, particularly for at-risk populations, to ensure adequate intake of key vitamins and minerals. A daily multivitamin in addition to dietary counseling is the most practical means of achieving this goal.

Angelo Tremblay, PhD, is a professor in the Department of Kinesiology at Laval University in Quebec City, Quebec, Canada.

Pamela R. Kushner, MD, is the director of Kushner Wellness in Los Alamitos, California, and a clinical professor of family medicine at the University of California, Irvine.

Financial Disclosure

Dr Tremblay reports having served as a consultant to Pfizer, Danone, General Mills, OmniActive Health Technologies, and Gelesis and having received grant support from Dairy Farmers of Canada, the Dairy Research Institute, and Nestlé.

Dr Kushner reports serving as an advisory board member for Pfizer, Eli Lilly and Co, Janssen, and AstraZeneca.


Medical writing support for this work was provided by James Street, PhD, and Diane Sloan, PharmD, of Peloton Advantage LLC and was funded by Pfizer.


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