(Dr. Mercola) Even when you eat a balanced, whole-food diet similar to the one presented in my nutrition plan, you may still fail to get the right balance of vitamins and minerals your body needs for optimal health. Because many factors contribute to your body’s ability to derive nutrients from the food you consume, you may eat a healthy diet and still lack proper nutrition.

Changes in animal feed, climate, farming and food-processing methods, soil conditions, water quality and weather patterns, as well as increased use of genetic engineering and toxic pesticides, can have a negative effect on the quality of food available.

Your age, genetics and health conditions such as digestive issues also impact your body’s ability to absorb nutrients from your food. Often, vitamin and mineral deficiencies can be difficult to identify because you may not develop symptoms until the deficiency has become quite pronounced.

Below, I comment on 10 of the most common nutrient deficiencies — ranging from vitamin A to zinc. As you review the list, take note of any deficiency symptoms that may apply to your current situation. Then, be sure to address any area of concern. In doing so, you will continue to protect and optimize your health.

No. 1: Vitamin D

The Harvard School of Public Health suggests an estimated 1 billion people worldwide have low vitamin D levels, with deficiencies noted across all age and ethnic groups.¹ You are at risk of missing out on vitamin D from natural sun exposure if you spend most of your time indoors, use topical sunscreens or wear long clothing for religious reasons. The signs and symptoms of vitamin D deficiencyinclude:

Achy or broken bones Because vitamin D helps your body absorb calcium, it plays a role in your bone health. Studies involving older adults have associated low vitamin D levels with an increased risk of falls and fractures.2

Age 50 or older At age 50, your kidneys may become less effective at metabolizing inactive vitamin D into its active form. At age 70 and beyond, your body will produce about one-third less vitamin D through sun exposure than it did at younger ages.

Body mass index > 30 Because vitamin D is fat soluble, when your fat cells uptake it, less is available for use elsewhere in your body.3 For this reason, some experts recommend you increase your intake of vitamin D if you are obese.

Dark skin Melanin, which determines your degree of skin pigmentation and protects your body from harmful ultraviolet radiation (UV), impairs your skin’s ability to produce vitamin D from sunlight. If you have darker skin, your body may need up to 10 times more sun exposure to produce adequate vitamin D as compared to a person who has lighter skin.

Feeling depressed or consistently having low energy Thanks to the brain hormone serotonin, your mood automatically elevates when you are in the sun. Researchers examining the effects of vitamin D on the moods of 80 elderly patients found the ones with the lowest vitamin D levels were 11 times more likely to suffer from depression.4

Frequent colds and flu A study done in Japan indicated schoolchildren taking 1,200 units of vitamin D per day during winter reduced their risk of contracting the flu by about 40 percent.5

Head sweating One of the classic signs of vitamin D deficiency is a sweaty head. Excessive sweating in newborns due to neuromuscular irritability is still described as a common, early symptom of vitamin D deficiency.6

If you are experiencing any of these symptoms, get your vitamin D level tested immediately. Even if you are in good health, I recommend you have your level tested twice a year. The optimal vitamin D level for general health ranges between 40 to 60 nanograms per milliliter (ng/ml). The ideal way to raise your vitamin D is by regularly and sensibly exposing large amounts of your skin, such as your arms, back, chest and legs, to sunshine. Getting outdoors at or around solar noon is the best time to soak up the sun.

If for whatever reason you cannot get outdoors, or not frequently enough to receive sufficient UV exposure, consider taking an oral vitamin D3 supplement along with vitamin K2 and magnesium. The only way to determine your ideal maintenance dose of vitamin D is by measuring your blood level. As a general guideline, vitamin D experts recommend 4,000 IUs per day for adults, but that level applies only if you are already in the therapeutic range. If your levels are low, you may need to start with 8,000 IUs or more per day.

No. 2: Omega-3s

If you regularly consume fast food and other highly processed foods, you probably overconsume inflammatory omega-6 fats. Such high consumption of omega-6s very likely means you may not be consuming enough of the healthier omega-3 fats. Processed foods — everything from frozen meals to salad dressings — are generally loaded with omega-6s, due to the vegetable oils used to make them.

Check labels carefully and do your best to avoid products containing corn, cottonseed, soybean, safflower and sunflower oils. If you are a regular consumer of fast food, be advised most of it is prepared with these same oils. Your recommended omega-6 to omega-3 balance should be close to a 1-to-1 ratio. However, because omega-6s are overabundant in the typical American diet, your ratio may be around 20-to-1, or as high as 50-to-1! It all depends on your eating habits.

Very often, when omega-6s predominate your diet, you will almost always suffer from inflammation and higher production of body fat. I suspect the high incidence of cancer, diabetes, heart disease, hypertension, obesity and premature aging noticeable worldwide may have its roots in the chronic inflammation resulting from this profound omega-3-to-omega-6 mismatch.

Omega-3s are anti-inflammatory and vital for supporting your brain function, joints, skin and vision, as well as your heart.^7,8,9 They are derived from both plant and animal sources:

• Alpha-linolenic acid (ALA): found in plant sources such as chia, flaxseeds, hemp and walnuts
• Docosahexaenoic acid (DHA): found in animal sources such as anchovies, salmon and sardines, as well as fish oil supplements; alternatives to fish oil include algae and my personal favorite, krill oil
• Eicosapentaenoic acid (EPA): also found in animal sources such as fish and fish oil, because wherever you find DHA, EPA is also there

I recommend an animal-based omega-3 because most of its cellular health benefits are linked to EPA and DHA, not the plant-based ALA. Although plant-based omega-3s are beneficial, and ideally you need both sources of omega-3, your focus should mainly be on the animal-based variety. To learn more about the critical differences between plant- and animal-based omega-3, and why they are not interchangeable, please see “The Critical Differences Between Omega-3 Fats From Plants and Marine Animals.”

In terms of supplementation, I believe krill oil is superior to fish oil. The omega-3 in krill is attached to phospholipids, which increase its absorption. Furthermore, compared to fish oil, krill oil contains almost 50 times more astaxanthin, a potent antioxidant that helps prevent omega-3s from oxidizing before they can be integrated into your cellular tissues. I cannot stress enough the importance of getting your omega-3 level tested.

No. 3: Magnesium

Because magnesium is the fourth most abundant mineral in your body, a deficiency can wreak havoc on your health. The fact researchers¹⁰ have detected more than 3,750 magnesium-binding sites on human proteins should give you a sense of how important this mineral is for your body’s optimal functioning. Your body needs magnesium for:

• Activating muscles and nerves
• Creating energy in your body by activating adenosine triphosphate (ATP)
• Helping digest proteins, carbohydrates and fats
• Serving as a building block for RNA and DNA synthesis
• Acting as a precursor for neurotransmitters like serotonin

Dietary sources of magnesium include avocados, Brazil nuts, brown rice, cashews, dark leafy greens like spinach and Swiss chard, oily fish, raw cacao, seaweed and seeds. Since there is no simple routine blood test to determine your magnesium level, it is best to get a magnesium RBC test, while also carefully evaluating and tracking your symptoms. You may be suffering from magnesium insufficiency if you experience:

• Constipation
• Eye twitches, muscle spasms — especially “charley horses” or spasms in your calf muscle that occur when you stretch your legs, numbness or tingling in your extremities and seizures
• Headaches and/or migraines
• High blood pressure, heart arrhythmias and/or coronary spasms
• Low energy, fatigue and/or loss of appetite

A few years ago, I interviewed Dr. Carolyn Dean, who has been studying magnesium for nearly 20 years. In her book, “The Magnesium Miracle,” Dean lists 100 factors to help you determine if you might be deficient. She also writes a blog, and you may find her post entitled “Gauging Magnesium Deficiency Symptoms” to be helpful.¹¹ Check out the short video below by Dean to learn more about why your body can’t live without magnesium.

No. 4: Iodine

Iodine is an essential mineral found in every one of your organs and tissues. Your body needs iodine for normal thyroid function, including the production of thyroid hormones, which support brain development, bone maintenance, growth and metabolism. Nearly one-third of the world’s population is iodine deficient.¹² Severe iodine deficiency can affect your child’s brain function and IQ. The most common symptoms you are not getting enough iodine include:

• Dry mouth, dry skin and lack of sweating
• Enlarged thyroid gland, also known as goiter, which contributes to a variety of cancers, including esophageal, breast, ovarian and thyroid
• Increased heart rate
• Shortness of breath
• Weight gain

Dietary sources of iodine include eggs, fish, raw milk, spirulina and sea vegetables such as kelp, kombu, nori and wakame. If you take an iodine supplement, be aware of the potentially serious risks associated with taking too much iodine. As a general rule, I do not advise taking large doses of iodine supplements like Iodora or Lugol’s long term.

In the video below, Dr. Jorge Flechas, a family physician from North Carolina who specializes in iodine therapy for thyroid and breast disorders, provides an informative overview of your thyroid, the incidence of thyroid problems and the importance of intaking sufficient iodine.

No. 5: Zinc

While you may think about it mainly during cold and flu season, zinc is an essential mineral found throughout your organs, tissues and bodily fluids. Moreover, after iron, zinc is the second most abundant trace mineral in your body. Because zinc is vital to many biological processes, you may not realize your body does not store zinc. Instead, you must intake it daily through the foods you eat or a high-quality supplement. Zinc supports your body’s critical processes such as:

Blood clotting	Immune function	Smell, taste and vision
Cell division	Thyroid health	Wound healing

At least 2 billion people worldwide are thought to be zinc deficient, including about 12 percent of the U.S. population and as much as 40 percent of the elderly.¹³ Part of the deficit likely results from soil depletion due to conventional farming methods, as well as the use of toxic pesticides such as Roundup. Beyond the soil concerns, many simply do not eat enough zinc-rich foods, the mineral is often poorly absorbed, levels are infrequently checked and testing methods are often inaccurate.

Dietary sources of zinc include dairy products, nuts, red meat and seafood. Plant sources such as asparagus, beans, green peas and spinach also contain zinc, but it is more easily absorbed from meat and animal proteins.

If you are an alcoholic or vegetarian, are pregnant or lactating, or have a digestive disorder or sickle cell disease, you are more likely to have a zinc deficiency. Even if you consider yourself to be a healthy person, you may not be eating enough zinc-rich foods on a daily basis to achieve optimal levels of this essential nutrient.

In the video above, I discuss the importance of zinc to your health, the signs of zinc deficiency and how you may improve your zinc levels through your dietary choices. Vegetarians have a particular challenge as phytic acid in grains compete with the absorption of zinc and other nutrients, which doesn’t occur in meat and dairy sources of zinc.

If you have symptoms of a zinc deficiency and choose to use a supplement, make sure it’s from a reputable company using best-practice, quality assurance methods. Independent verification of the raw materials is vital to confirm quality and assure it is free of lead and other heavy metals. The supplement should contain several different types of zinc, such as gluconate, citrate and chelate. Unless your clinician recommends otherwise, don’t go above 40 mg per day.

No. 6: Vitamin B12

Vitamin B12 (cobalamin) is known as the energy vitamin, and you need it for blood formation, DNA synthesis, energy production and myelin formation. You may be deficient in vitamin B12 if you are not eating enough of the foods containing it, or your body lacks the ability to absorb it properly.

According to the U.S. Department of Agriculture, nearly 40 percent of the American population may have marginal vitamin B12 status¹⁴— not low enough to qualify as deficiency, but low enough to where certain neurological symptoms may start to appear. Warning signs of a B12 deficiency are slow to appear, so you may be quite deficient by the time you recognize the symptoms, which include:

Apathy	Memory problems and/or “mental fog”	Muscle weakness
Fatigue	Mood swings	Tingling in the extremities

Vitamin B12 is present in its natural form only in animal sources of food, such as:

• Grass fed beef and beef liver
• Lamb
• Venison
• Organic pastured eggs and poultry
• Seafood such as salmon, scallops, shrimp and snapper

If you are a strict vegetarian or vegan, you are at increased risk of B12 deficiency. While you can get some B12 from coconut oil, fortified coconut milk and nutritional yeast, you may need to take a daily supplement. Chronic long-term B12 deficiency can lead to serious conditions such as dementia, depression and fertility problems.

Most B12 supplements sold today are a waste of your money because B12 does not absorb well. Your best option is to supplement with a B12 spray, which I think is better than receiving painful B12 shots from your doctor. Whether you choose animal foods or a high-quality spray, if you are a vegan, you should consider increasing your consumption of B12 to avoid future health problems.

No. 7: Vitamin E

Vitamin E is an important fat-soluble vitamin and antioxidant designed to combat inflammation and make red blood cells. It also helps your body use vitamin K, which is important for heart health. Six billion people worldwide and 75 to 90 percent of Americans are deficient in vitamin E.¹⁵ If you are among them, you are at increased risk for cardiovascular disease, cognitive deterioration and immune dysfunction.

To achieve an optimal level, you need at least 50 IUs of vitamin E daily. The recommended dietary allowance for anyone 14 years or older is 15 milligrams (mg) per day. Vitamin E is well-known for protecting against free radical damage and the effects of aging. It is actually a family of at least eight fat-soluble antioxidant compounds, divided into two main categories:

• Tocopherols, which are considered the “true” vitamin E
• Tocotrienols, each of which has subfamilies of four different forms

Vitamin E can easily be obtained from a healthy diet, and high amounts of it are found in three general categories of foods:

• Leafy greens like spinach
• High-fat foods such as nuts, seeds, fatty fish and seafood, including sardines and shrimp
• Oil-rich, high-fat plants such as avocados and olives

Most of these foods are best eaten raw because cooking will destroy some of the nutrients. Obvious exceptions exist of course — do not eat raw shrimp, for example. If you must use a supplement, choose a full-spectrum vitamin E containing mixed natural tocopherols and tocotrienols. Avoid the synthetic form. Natural vitamin E is always listed as the “d-” form: d-alpha-tocopherol, d-beta-tocopherol, etc. Synthetic versions are listed as “dl-” forms.

No. 8:  Vitamin K2

Vitamin K is a fat-soluble vitamin that is well-known for its role in blood clotting. However, there are two different kinds of vitamin K,¹⁶each providing its own set of health benefits. Vitamin K1 is primarily responsible for blood clotting whereas vitamin K2 works synergistically with calcium, magnesium and vitamin D to impart a number of important health benefits.

Vitamin K2 also plays a crucial role in bone health,¹⁷ and may be critical for the prevention of osteoporosis (brittle bones). Osteocalcin is a protein produced by your osteoblasts (cells responsible for bone formation), and is utilized within the bone as an integral part of the bone-forming process. However, osteocalcin must be “carboxylated” before it can be effective. Vitamin K functions as a cofactor for the enzyme that catalyzes the carboxylation of osteocalcin.

If you do not have sufficient amounts of vitamin K2, you run the risk of both brittle bones and calcification in your soft tissues. In other words, vitamin K2 is necessary to keep your bones strong and your soft tissues pliable. A number of Japanese trials have shown that vitamin K2 completely reverses bone loss and in some cases even increases bone mass in people with osteoporosis.¹⁸

The pooled evidence of seven Japanese trials also show that vitamin K2 supplementation produces a 60 percent reduction in vertebral fractures and an 80 percent reduction in hip and other non-vertebral fractures.¹⁹ One Chinese meta-analysis²⁰ of 19 randomized controlled trials found that vitamin K2 supplementation significantly improved vertebral bone density in postmenopausal women and reduced the risk of bone fractures.

Another three-year-long placebo-controlled study²¹ done in the Netherlands found that postmenopausal women taking 180 mcg of MK-7 per day increased their bone strength and saw a decrease in the rate of age-related bone mineral decline and reduced loss of bone density, compared to those taking a placebo. The following graphic, from a 2014 research paper²² on vitamin K2, illustrates the dual effect of vitamin K on bone and vascular health.

Vitamin K2 is found primarily in animal-based foods (MK-4) and fermented foods (MK-7). However, when it comes to MK-7, it’s important to realize that not all bacteria make K2, so only certain fermented foods will contain it. Grain fed animals will also produce far lower amounts of K2, and are best avoided for other reasons. Only grass fed animals will develop naturally high K2 levels.

For these reasons, most commercial yogurts are virtually devoid of vitamin K2, and while certain types of cheeses, such as Gouda, brie and Edam are high in K2, others are not. One of the best ways to get plenty of vitamin K2 from your diet it is to regularly eat home-fermented vegetables made with a special starter culture designed with bacterial strains that produce vitamin K2.

You can get up to 500 mcg of vitamin K2 in a 2-ounce serving of fermented vegetables using such a starter culture, which is a clinically therapeutic dose. This is also one of your most economical alternatives.

No. 9: Selenium

Selenium serves two very important and interrelated roles:

1. At the cellular level, selenium is an active component of glutathione peroxidase, an enzyme that converts hydrogen peroxide to water. Glutathione peroxidase has potent antioxidant properties, and serves as a first line of defense against build-up of harmful free radicals in your cells.
2. Selenium also plays an important role in the prevention of cancer. One of the reasons people get cancer is because of excessive free radical production. By reducing free radicals, selenium helps reduce your risk of cancer.

If you like Brazil nuts, eating about two to three of them per day will typically be sufficient. If you opt for a supplement, make sure to get the correct form. What you’re looking for is the high-selenium yeast form, the scientifically tested and most recommended version.

No. 10: Vitamin A

Nearly half of American adults and teens are at risk for insufficiency or deficiency of vitamin A.²³ Your body needs a daily dose of this fat-soluble vitamin to maintain healthy bones, cell membranes, immune function, skin, teeth and vision. Vitamins A and D work in tandem, and there’s evidence suggesting that without vitamin D, vitamin A can be ineffective or even toxic.

On the other hand, if you’re deficient in vitamin A, vitamin D cannot function properly either, so a balance of these two vitamins is essential to good health. That said, because we do not yet know the optimal ratios between these two vitamins, balancing them well through supplementation can be challenging. For that reason, if you are able, it’s best to intake vitamins A and D from food and sun exposure, rather than supplements.

The best source of vitamin A your body can actually use is animal products such as fish, grass fed meat, liver and pastured poultry, as well as raw, organic dairy products like butter. These foods contain retinol, preformed vitamin A that your body can easily use. You will find it difficult to get sufficient amounts of vitamin A from beta-carotene, a provitamin A found in plant foods like broccoli, cantaloupe, carrots, squash and sweet potatoes.

While your body can readily use the retinol form of vitamin A, it must convert provitamin A (carotenoids) into bioavailable retinol. If you’re in excellent health, this should not pose a major problem; however, factors such as alcohol use, digestive problems and genetics can affect your body’s ability to absorb carotenoids and convert them into retinol. Medical conditions that interfere with the digestion of fat, including Crohn’s disease, cystic fibrosis and gallbladder and liver disease also affect your body’s ability to convert vitamin A.

A number of studies have raised warnings about vitamin A supplementation; indicating high doses may lead to toxicity, and may raise your risk of cancer, heart disease and all-cause mortality. Be particularly cautious with retinol or retinoic acid supplements, as these fat-soluble forms pose a greater risk of toxicity. Strictly avoid all synthetic versions.