Poor or inadequate diets are linked to four of the top 10 causes of death: heart disease, cancer, stroke, and diabetes. During a nutritional intake assessment, the Healthy Eating Index for 1999-2000, researchers for the Center for Nutrition Policy and Promotion noted that only 10% of the U.S. population had an adequate diet, 74% had inadequate nutrient intake, and 16% were rated to have a poor diet, markedly increasing the risk for major health problems.

To be clinically significant, a deficiency needs to be common and the adverse impact of that deficiency needs to be strong. But identifying deficiencies is challenging, as controversy exists regarding whether nutritional deficiencies should be based on “optimal intake” and, if so, what optimal intake should be. The recommended daily allowances (RDAs) the government has established do not clarify optimal nutritional intake; rather, they are calculated to estimate levels necessary to prevent a disease state in 98% of healthy people, depending on their age and gender.

Optimal nutrient intake for immune function, cardiovascular health, and osteoporosis prevention are clearly higher than the RDAs involved. This article does not hope to resolve the controversies related to optimal intake and precise dosing, but it does aim to highlight important deficiencies that can be easily corrected and would result in substantial improvements in health.

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The clinically important deficiencies in are ranked in an order approximately reflecting magnitude of benefit if they were to be corrected. Of interest, the top five deficiencies cannot be remedied by adding a multivitamin. A high-quality daily multivitamin would, on the other hand, resolve deficiencies listed sixth through 10th. We focus here, then, on only the top five.

Deficiency #1: Fiber

The most clinically important deficiency in the American diet is fiber. Fiber intake in the United States averages 12-15 g daily, while nearly all recommendations suggest 30-50 g. Fiber consumption is inversely associated with insulin levels, weight gain, GI function and disease, and many cardiovascular disease risk factors (central adiposity, BP, HDL and LDL, fibrinogen, and triglycerides).

Fiber comes in two forms—insoluble and soluble. Both forms are essential. They reduce calorie intake by improving satiety with eating and are associated with good weight control. Insoluble fiber (good sources are whole grains) enhances GI function and is packed with nutrients. Soluble fiber (found in fruits, vegetables, oats, nuts, and beans) lowers cholesterol and blood sugar levels and is also loaded with nutrients.

At least half of the 30 g of fiber intake daily should come from fruits and vegetables. Individuals should consume the equivalent of at least five cups of fruits and vegetables (two pieces of fruit, a salad, a couple cups of colorful vegetables for lunch, dinner, and snacks).

Increasing soluble and insoluble fiber intake is clearly an achievable goal and would have an enormously beneficial impact on public health.

Deficiency #2: Long-chain omega-3 fats

Long-chain omega-3 fats, e.g., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), come from seafood and have been shown to have multiple clinical benefits. They reduce triglyceride levels and clot formation, improve insulin sensitivity, and lower inflammation in patients with Crohn’s disease and rheumatoid arthritis.

Several studies have shown that long-chain fatty acids decrease the risk for cardiovascular events and reduce mortality. In terms of reducing cardiovascular events, increasing omega-3 fat intake is more important than cutting saturated fat intake.

Omega-3 fats also appear to decrease the incidence of Alzheimer’s disease (AD). Not only is the brain 40% omega-3 fat by weight, making fish oil an essential brain component, but inflammation and abnormal blood sugar regulation increase the risk for AD and both are improved with regular fish-oil intake. Fish oil has also been shown to enhance brain-cell formation and synaptic function.

Medium-chain omega-3 fatty acids from plants will lower cholesterol levels, but they do not have the same proven benefits as marine-derived long-chain omega-3 fatty acids. Soy-based foods, ground flax seed, and nuts are all healthy sources of medium-chain fatty acids, as well as fiber and other nutrients.

Fish-oil dosing varies with the indication. One gram daily, obtained from eating cold-water oily fish three times a week, provides the amount of fish oil needed to enhance blood sugar metabolism, reduce the risk of arrhythmias, and lower AD risk. Higher dosages (2-4 g daily) are required to lower triglyceride levels and reduce inflammation adequately to treat disk herniations and arthritis symptoms.

Good sources of marine omega-3 fats include salmon, sardines, sole, herring, and trout, plus cold-water oysters and mussels. Canned wild salmon and herring are the healthiest and least expensive sources.

While seafood provides many benefits, one of the concerns related to seafood consumption is mercury intake. Fortunately, many marine foods high in omega-3 fats are low in mercury. Follow these two rules: Cold-water fatty fish are high in omega-3 fat; large-mouth fish are high in mercury.

Thus, keeping tuna, grouper, snapper, and bass to fewer than two to three servings a month and swordfish, kingfish, and shark to no more than a few servings a year eliminates most of the excessive intake of mercury.

For people who don’t eat fish or for those requiring a higher dosage of fish oil, supplements are convenient though fairly expensive. Most brands should be free of heavy metals, but many commonly sold brands are rancid, result in foul burping, and, by increasing lipid peroxide levels, may actually produce harm that has not yet been assessed in clinical trials.

To ensure low rancidity, fish oil should be palatable. Consumers can judge quality by poking a needle in the first capsule from each bottle and tasting the contents. The best brands provide a choice between fish oil sold as a liquid or the same oil sold in capsules.

One caution with fish oil is that dosages >2 g daily mildly increase bleeding risk. In particular, patients scheduling surgical procedures should stop high fish-oil dosing at least one week prior, and those being treated with anticoagulation (beyond aspirin daily) should have some risk/benefit counseling regarding rare bleeding risk before taking >2 g daily.

Deficiency #3: Vitamin D

Vitamin D functions as a hormone, and every cell in the human body appears to have vitamin D receptor sites. Vitamin D is well known to enhance calcium absorption and is essential for maintaining bone density. Less well understood is the role of vitamin D in immune function, but low levels of vitamin D are strongly associated with an increased risk for both autoimmune diseases (especially multiple sclerosis [MS]) and cancer. Vitamin D inhibits proliferation of benign and malignant tumor cells, such as those that may occur in the colon, prostate, or breast.

Sixty-two percent of elderly women’s diets are deficient in vitamin D, and 32% of young adults had deficient vitamin D levels (on blood determinations) during winter.

Compounding dietary deficiency is the reduction of sun exposure for many Americans. Adequate sun allows the skin to synthesize vitamin D from cholesterol, but sunblock prevents this production and concerns regarding both skin cancer risk and skin aging have led many to greatly decrease sunshine exposure.

Enormous controversy surrounds the currently recommended intake for vitamin D; 200 IU has been shown to prevent rickets and is the amount noted on nutrition food labels. However, at this intake level, rates for MS, severe osteoporosis, and many forms of cancer increase substantially. Most data suggest that 1,000 IU daily is the evidence-based intake to minimize disease risk, and up to 3,000 IU daily has an excellent safety record.

The good news is that vitamin D deficiencies can be easily eradicated at minimal expense if patients ensure adequate intake. Daily intake of 1,000 IU of vitamin D can be achieved by combining dietary sources and including a multivitamin with adequate intake of other commonly deficient nutrients, in particular calcium and fish oil. Adding limited sunshine exposure also helps.

There are times when vitamin D levels should be measured to clarify a diagnosis or to optimize dosing. Specific situations for testing include suspicions of rickets, severe osteoporosis, MS, or other poorly controlled autoimmune disorders. To measure vitamin D levels, a 25-hydroxyvitamin D (not 1,25-dihydroxyvitamin D) level should be ordered from a blood draw. Many laboratories now list 30 ng/mL as normal, although the most common expert-opinion goal is at least 40-70 ng/mL, with 100 being the upper end of the normal range.

Deficiency #4: Magnesium

Magnesium is required for more than 300 chemical reactions in the human body, affecting cardiac function, bowel function, blood sugar control, BP, and bone health. Not surprisingly, then, magnesium deficiency plays a role in cardiac deaths, poor BP control, and GI problems, in particular constipation.

About half of magnesium stores are intracellular, and half are combined with calcium and phosphorus in bone. Only 1% of magnesium is found in blood; thus serum magnesium levels are a poor reflection of magnesium stores, and the simplest measure would be RBC magnesium levels.

The RDAs for magnesium are determined by age:  In males, the RDAs are: ages 14-18—410 mg; ages 19-30—400 mg; ages 31 and older—420 mg. For females, the RDAs are: ages 14-18—360 mg; ages 19-30—310 mg; and ages 31 and older—320 mg. The RDA increases by 40 mg during pregnancy.

Good dietary sources of magnesium include green leafy vegetables, whole grains, nuts and seeds, wheat and oat bran, and soy products.

Not only are 75%-85% of U.S. diets deficient in magnesium (the average diet contains only 50%-60% of the RDA), but several common factors lead to magnesium depletion, including diuretic use, elevated glucose levels, diarrhea, alcohol intake, and malabsorption related to GI diseases.

Complicating magnesium deficiency is that adding calcium supplements alone blocks magnesium absorption and worsens what is already a national magnesium deficiency problem. This problem is made worse by the lack of quality clinical outcome studies identifying the optimal calcium/magnesium supplement recommendation, but expert opinion regarding combining these supplements ranges from a 2:1 to 3:1 calcium/magnesium ratio.

Symptoms associated with magnesium deficiency include muscle cramps, tingling, numbness, abnormal heart rhythms, coronary spasm, seizures, confusion, disorientation, loss of appetite, and depression.

Magnesium is commonly supplemented in the form of magnesium oxide, but this frequently acts as a GI irritant and many people complain of GI upset with adequate dosing. Better-absorbed and better-tolerated forms of magnesium would include chelated magnesium (protein-bound rather than salt-bound) or magnesium citrate or magnesium glycinate.

Deficiency #5: Calcium

Calcium is well established as essential for bone health and is associated with membrane stability, impacting BP control and cardiac function. More recently, calcium deficiency has also been associated with weight control and metabolic rate.

Calcium deficiency is of high clinical importance, as the average diet contains only 40%-50% of the RDA (800-1,200 mg daily, varying with age and gender). Intake of 1,500 mg daily is recommended for people with osteopenia or osteoporosis. More than 2,000 mg of calcium daily is excessive and has been associated with an increased cancer risk.

Too often, physicians recommend calcium supplementation without assessing dietary calcium intake, which leads to inappropriate calcium dosing. Subtracting the amount of calcium in foods ingested from the patient’s calcium intake goal will yield the amount of calcium that must be provided from either a supplement or a daily food source.

It is not feasible to put an adequate amount of calcium into a multivitamin. Thus calcium needs to be consumed in food or may require several calcium pills daily to reach the recommended intake.

The most commonly sold calcium supplement is the inexpensive calcium carbonate, which is popular, as it creates the smallest pill size. However, it must be taken with food to be absorbed, may contain lead, and is associated with GI symptoms, including constipation.

The best absorbed form of calcium not associated with GI problems is protein-bound or chelated calcium, but it is more expensive and twice the size of calcium carbonate pills, requiring a high pill count to achieve the same dose. Calcium citrate is less constipating than calcium carbonate and does not need to be taken with food, but it remains a large pill, like protein-bound calcium. Calcium citrate is not as well absorbed as protein-bound calcium but is intermediate in price.

With proper guidance, most Americans can achieve proper calcium intake.

Dr. Masley is a family physician and a certified nutritionist with a clinical practice in St. Petersburg, Fla. He is also a clinical assistant professor with the University of South Florida in Tampa. He can be reached at www.drmasley.com.