Do I need to have blood tests to find out what vitamins to take?

Patients often come in asking “should I get blood testing for vitamin levels?”As physicians we can not argue that testing blood levels of certain vitamins has a role. However, we have found in our many years of practice that vitamin levels are far from necessary in most people.

We often hear of people going to various naturopathic or functional medicine physicians who order extensive (and expensive!) panels of endless levels of various vitamins, hormones and other items. Typically the results of these multitudes of levels then dictates the prescribing of many expensive (and often unproven supplements). But, buyer be ware! If something seems over the top it probably is. The medical data suggests that too much testing is overkill and a few key levels have their role and can be useful to health care. Blood testing for many vitamins is often not accurate or useful. For example, magnesium levels are often inaccurate and not reflective of true need.

The most common vitamin levels that are checked include vitamin D, vitamin B12 and iron.  And yes, it’s true that many people are deficient in these nutrients! However, checking levels is often not necessary or that helpful in telling us this. It turns out that it’s usually fairly easy to predict who is deficient in which vitamin based on various factors including age, diet, lifestyle and health issues.

We often joke that we can predict your vitamin D from a mile away if we know that you live in our very vitamin D deprived Chicago climate.  The key is using these factors to then determine how much vitamin D you need to be taking on a daily basis to help correct this deficiency and maintain an optimal level.  It turns out that we do not all have the same needs.  In addition to where you live, things like race (skin pigment affects vitamin D absorption) diet and other factors help determine these needs. Taking a proper dose of D is essential since taking too much can also cause significant harm.

We often see vitamin B12 deficiency in people who keep a vegetarian or vegan diet.  In addition certain people as they get older can benefit from b12. The challenge with B12 blood levels, is they are not always accurate and can often be normal despite deficiency.  Some times the low end of normal is actually low. In general taking a b12 oral supplement in those who we suspect deficiency or need based on their diet, lifestyle and health concerns, is the way to go. However, there are rare cases of people with extreme needs, typically those who have had portions of their GI tract removed or bipassed  (such as after gastric bipass surgery), had major intestinal illnesses such as Crohn’s disease or with intestinal absorption issues such as celiac disease. These are people who at times need to take B12 either sublingually or via injection if oral supplements do not suffice.

And last but not least, iron levels. Iron levels can be of use but are done rarely. More commonly we run blood counts, which can show if someone is anemic. Many physicians and health practitioners falsely assume that a normal hemoglobin on a CBC means that you do not need to take iron. It turns out that many of the patients we see are not in anemic but they do have low total body iron stores as seen when measuring a ferritin level. Most of the women we see do have low ferritin levels likely because their iron supplies have been depleted from years of having periods, pregnancies and nursing babies. They tend not to eat red meat (best dietary source of iron) in the quantities needed to build back up iron stores. Men too often have low ferritin levels, perhaps due to less red meat consumption or iron absorption.  Many people do not recognize the symptoms they are having from low iron (including low energy, thinning hair or hair loss, fatigue, brittle nails). Repleting iron depends less on the actual iron levels and more on finding a tolerable form of iron to take. Many people get side effects from certain oral iron preparations, thus finding the right form of iron as well as pairing it with the other nutrients to help absorption is key.

Another misconception about blood testing is in regard to calcium. Patients often want to know how much calcium they should be taking based on blood testing that includes a serum calcium. Calcium levels in the blood do not reflect if you are getting adequate calcium intake. Your body should maintain a normal serum calcium no matter your diet. It will however, leech calcium from your bones if you are not eating enough calcium. This is why getting enough calcium in your diet is essential (and a supplement when necessary) but blood testing is of no value in determining this. Find out more about calcium intake here.

In short, when people ask us “Do I need to get blood tests to find out what vitamins I need to take?”, the answer is typically, “No.” Blood testing rarely changes what we recommend for you based on your diet, lifestyle and specific symptoms. When it comes to deciding what vitamins you need and in what quantities there is no substitute for the details of who you are, what you eat, and your health conditions.  We created personalized multivitamins to address individual needs based on these factors. Most people fall short on certain nutrients which can be predictably determined by your answers to key questions. There are extreme cases where people fail normal vitamin replacement and vitamins levels can then be used to influence treatment. Take our personalized vitamin quiz.


Romy Block specializes in Endocrinology and Metabolism and is mother to three active adolescent boys. Arielle Levitan is a Doctor of Internal Medicine with a special interest in Preventive Medicine and Women’s Health.  She is a mother of three teen agers. As professional women with active family lives, they recognize that people often neglect their own health needs and are uncertain about what vitamins to take. Each person is different in her diet, exercise and health history, and will benefit from different nutrients.  After years of advising their patients about the proper vitamins to take,  Drs. Block and Levitan created Vous Vitamin® to provide people everywhere with quality vitamins that are suited to their individual needs. They are authors of the award winning The Vitamin Solution: Two Doctors Clear Confusion About Vitamins and Your Health (She Writes Press, 2015). Take your vitamin survey now to get exactly the right vitamins for your needs.

The statements made in this article have not been evaluated by the Food and Drug Administration. The products offered by Vous Vitamin® are not intended to diagnose, treat, cure, or prevent any disease.

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