Svg Vector Icons : Store
Health Concerns
Top 3 Reasons You Don’t Feel Good After You…

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

7 Signs You Have a Hormonal Imbalance

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

How To Heal Leaky Gut in 5 Easy Steps

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

The Gene Mutation That Affects 40% of People

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

8 Ways to Get Over the Flu Fast

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

Biohack Boozing: Your Complete Guide

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

Recipes & Nutrition
What Are the Benefits of Celery Juice? A Doctor…

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

5 Reasons to Take a Magnesium Supplement

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

5 Natural Herbs and Supplements to Increase Sex Drive…

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

Welcome to Parsley’s New NYC Center

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

10 Reasons You Need A Better Doctor

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

5 Essential Blood Tests You Need Every Year

Even if you are super health-conscious, busy schedules and the demands of modern life can make…

Food & Nutrition

5 Most Common Nutrient Deficiencies Explained

Even if you are super health-conscious, busy schedules and the demands of modern life can make it hard to get all the nutrients you need from diet alone.

Many people take a multivitamin to “be on the safe side”. They hear that the soil our food is grown in is no longer nutrient-dense or worry that their diet isn’t as healthy or diverse as it should be, so assume they should take a multivitamin.

The reality is that for most people, if your diet is varied and filled with a rainbow of fruits and vegetables, and you are healthy and absorbing nutrients well from your gastrointestinal tract, you probably don’t need the extra vitamins and minerals.

So how do you know if you’re deficient?

The best way to find out is to see your physician and have a blood test to check your levels. At Parsley Health, we remove the guesswork by measuring many of these nutrients with in-depth blood tests. We then use this information to create a personalized plan for each member that uses lifestyle changes, supplements and medications when necessary to treat the root cause of their symptoms.

Below are some of the most common symptoms that you may have a specific nutrient deficiency:

  • General lethargy, tiredness, aches, and pains
  • Increased anxiety and restlessness
  • Brittle hair and nails
  • Irritability
  • Depression
  • Brain fog
  • Acne

While this is not an exhaustive list, it’s also important not to pass off these symptoms as normal parts of life. Instead, they are often clues that something deeper is going on in the body.

Top 5 nutritional deficiencies.

Here’s a look at the most common nutrient deficiencies that contribute to everything from fatigue, migraines, and hormonal imbalances, what this means for your overall health, and how you can address them.

Vitamin D

Vitamin D gets top billing because almost every single person we see at Parsley Health is deficient in this vitamin. Of course, a key question to address is what qualifies as a deficiency.

You’d think the answer would be straightforward, but it’s most definitely not. In 2011 the Endocrine Society issued a report recommending a vitamin D level of 30ng/mL, and because of inconsistencies with testing, suggested aiming for a level of 40-60ng/mL. But then some top doctors in the field said the minimal level should be decreased to 12.5ng/mL because only 6% of Americans have levels below that. In other words, they suggested we just lower the bar for what is considered deficient, and then we won’t have so many people low in vitamin D.

While it’s true that we can get Vitamin D from the sun, most of us wear clothing that covers most of our bodies, use sunscreen, and spend the majority of our time indoors. Since sunlight on exposed skin is the primary source of vitamin D, we simply don’t get enough.

Levels as low as 20ng/mL are going to be enough to prevent rickets, but some of the studies of vitamin D and risk for various cancers, cardiovascular disease, certain autoimmune diseases, falls and depression suggest that you need a level somewhere between 40-60ng/mL. (2, 3) At Parsley Health we aim for levels slightly above that, 50-70ng/mL which is also well below any risk for vitamin D toxicity. We also have our own Vitamin D optimized for maximum absorption.


Magnesium comes next not only because people are frequently deficient in it, but also because its value in wellness is often underappreciated. Magnesium’s most crucial role is in helping with brain, heart and muscle function. But its function in the body extends far beyond that. It is involved in the synthesis of DNA and RNA, and proteins, and is a critical factor in at least 600-800 enzymatic reactions.

It is no wonder that severe deficiency can lead to conditions such as arrhythmias, abnormal muscle contractions, seizures and delirium. For people with suboptimal levels of magnesium, the consequences may be as varied as hypertension, menstrual cramps, migraines, osteoporosis and muscle cramps. (4)

To ensure people have enough magnesium to keep these critical organs functioning well, doctors generally measure magnesium in the serum (the non-cellular part of the blood) and usually, it is in the normal range. However, this only represents an estimated 1% of total magnesium stored in the body. (5)

To get a better sense of how much magnesium is truly in the body, the doctors at Parsley Health measure the amount of magnesium in red blood cells. When these total magnesium levels are considered, about 15% of people are deficient and another 34% have suboptimal levels. (6)

The main causes of magnesium deficiency include:

  • Our soils have become depleted of nutrients, which has led to less nutrient-dense produce.
  • Grains, a good source of magnesium, lose most of their magnesium when they are refined.
  • Also, medications are to blame: antacids decrease absorption and diuretics increase urinary excretion.

Some good dietary sources of magnesium are nuts, seeds, leafy greens, whole grains, beans and fish. It may also be helpful to use a high-quality magnesium supplement.


If magnesium is underappreciated, iodine is downright ignored. Ever since iodine was added to table salt, people in developed countries have stopped giving this mineral its due attention. Although iodine deficiency is much less common in developed countries, it is still an issue, with about 10% of the population in the Americas and 52% of Europeans deficient. (7) In the US, 15% of women of reproductive age are deficient. (8) What qualifies as adequate is questionable, as the US RDA is 150mcg/day, while in Japan the typical intake is 1000-3000mcg/day.(9)

Iodine is one of those Goldilocks nutrients – you have to be careful you don’t get too much or too little. If you are severely deficient you could develop hypothyroidism, but even modest deficiencies may be problematic. Iodine is taken up by the thyroid, stomach lining and mammary glands and getting enough iodine may decrease risk for cancer in each of these organs. (10, 11)

On the other hand, too much iodine may also increase your risk for autoimmune thyroid disease, which is seen in these very same countries. (13) Measuring iodine in the body accurately isn’t easy, but a good place to start is with the blood. For a clearer picture, you can collect your urine for 24 hours and measure the amount of iodine in it.

At this point, I don’t think anyone can pinpoint the optimal amount of iodine, but including a seaweed salad, a sprinkle of dulse on your greens, or some kombu in your soup a few times per week is a good way to increase your intake without going overboard, and at the same time you’ll be getting the myriad of other nutrients found in sea vegetables. Just be aware that nori, the seaweed used to wrap sushi, is the least nutritious, and kelp, which is sometimes used as a salt substitute, is extremely high in iodine.

Schedule a free call to learn how we've helped our members reduce prescription drugs by 7x.

Vitamin B12

Vitamin B12 is abundant in animal food but practically non-existent in plant foods. That’s why we expect our vegan members to have low levels of this nutrient and need to take a supplement. However, what’s surprising is that many people who eat animal protein on a daily basis are also low in vitamin B12.

As is true for most nutrients, assessing what is a sufficient level is not as straightforward as we’d like it to be. It is clear that people with blood levels of B12 < 150pg/mL are deficient, but plenty of people with levels higher than that still have inadequate stores of B12, so a level between 150-400 pg/mL is considered borderline.

Even if a B12 level falls in the normal range, we can get a better idea of who is low in B12 at a tissue (cellular) level by measuring homocysteine and methylmalonic acid; one or both rise if there is an insufficient amount of B12 in the body. (15)  At Parsley Health, we cover our bases by aiming for a B12 level > 400pg/mL, and also measuring homocysteine and methylmalonic acid in all of our members.

There are a number of causes of B12 deficiency besides a vegan diet, including:

  • Low stomach acidity.  Stomach acid is needed to separate B12 from the food protein it is attached to when swallowed. (16)  Of course, acid-blocking medications decrease stomach acidity, and it often decreases simply in the course of aging.
  • Pernicious anemia. This is an autoimmune disease that interferes with the absorption of vitamin B12.(16)
  • Small intestinal bacterial overgrowth (SIBO). The bugs that mistakenly take up residence in the upper part of the small intestines in SIBO consume some of the B12, so less reaches the lower part of the small intestines (ileum) where B12 gets absorbed into the bloodstream. (17)
  • Metformin. This is the most common medication used to treat type 2 diabetes and can interfere with B12 absorption into the bloodstream.
  • MTHFR mutation. There are genetic variations in this gene that don’t affect B12 absorption but can affect its utilization in the cells.  (See a recent blog on this topic:

The most severe consequences of B12 deficiency are:

  • Hematologic: low red cells, white blood cells and/or platelets. (18)
  • Neurologic: degeneration of the spine and/or peripheral nerves, often beginning with numbness in the toes and working its way up the legs. (18)
  • Psychological symptoms: cognitive difficulties, paranoia, hallucinations, depression or anxiety. (19)

The good news is that if you aren’t eating or absorbing enough B12, you can take it in the form of a pill or an injection.


Of all the nutrients in this list, iron is the most straightforward. We measure the stored form of iron with a blood test called ferritin, and can also measure the actual amount of iron circulating in the blood. The prevalence of iron deficiency ranges from 2% in men to 20% in black and Mexican-American women. (20)

Iron comes from both plant and animal food. Plant sources of iron (called non-heme iron), such as leafy greens, legumes, nuts and seeds, are not as easily absorbed as the animal sources (heme iron). So vegetarians and vegans are at higher risk for iron deficiency than omnivores.

In addition, menstruating women, especially those with heavy periods, can have low iron stores. Finally, anyone who bleeds, whether it’s a slow, steady blood loss from gastrointestinal diseases such as an ulcer or cancer, or a more rapid loss from an injury or surgery, can end up iron deficient, as they use up their iron when they have to make a lot of new red blood cells.

A minimum level of ferritin is somewhere between 12-20ng/mL. Levels less than that often lead to iron deficiency anemia, with its associated symptoms, including fatigue, weakness and cold extremities. But even levels that aren’t low enough to cause anemia can still cause other problems, such as restless leg syndrome, hair loss, brittle or spooning of the nails, loss of sense of smell,(21) and hypothyroidism. (22)

Fortunately, it is easy to increase your iron levels either by eating red meat (ideally organic and grass fed) or taking an iron supplement. And if necessary, intravenous iron replacement is also an option.

Parsley’s medical plans include personalized testing to help you identify nutrient deficiencies. Join Parsley today.

Final thoughts on nutritional deficiencies.

The nutrient deficiencies described above are the ones we most commonly see at Parsley Health, but of course, all vitamins and minerals are critical for good health, along with all the other nutrients scientists have identified or have yet to identify. Rather than trying to guess your levels of these and other nutrients, get yourself tested and always consult your physician before taking any new supplements to address any deficiencies you think you may be dealing with.

Do you still have questions about the in-depth testing we do to help our members treat and address vitamin and mineral deficiencies? If this is something you’d like to learn more about, consider booking a free 15-minute consult call with our team here.

Fuel your body and fill in nutritional gaps with Dr. Berzin’s Daily Essentials Kit.

Shop now



Parsley Health is the only medical practice that leverages personalized testing with whole body treatments.

More Food & Nutrition

Food & Nutrition
Everything You Need to Know About Protein Powder

Protein is an essential part of a balanced diet, and depending on your diet, sometimes you…

Gastrointestinal Issues
Gut Healing Bone Broth Recipe

Bone broth is not a new concept, but it has recently been rebranded as a modern…

Food & Nutrition
The 5 Must-Have Ingredients for Spring

Spring is the time of year when nature is waking up from a long winter’s rest…

Food & Nutrition
13 Genius Tips for Eating Healthy on A Budget

Cleaning up your diet? There is a misconception that eating healthy is expensive, but there are…

Find out if Parsley is perfect for you. Schedule a free call with one of our health care advisors.