Vitamin D: Guide to Deficiency Symptoms, Foods, Benefits, and More

Integrative & Functional Medicine Physician By Alejandra Carrasco, M.D.
Integrative & Functional Medicine Physician
Alejandra Carrasco, M.D., is an integrative and functional medicine physician, best-selling author of Bloom, and founder of Nourish Medicine, a root-cause resolution integrative and functional medicine practice in Austin, Texas. She received her Master's from the University of Texas Health Science Center.
Vitamin D: Guide to Deficiency Symptoms, Foods, Benefits, and More

Photo by Susana Ramírez

Unless you live in the tropics year-round or take supplements proactively, chances are you aren’t getting enough vitamin D. And despite widespread educational campaigns to raise awareness, vitamin D deficiency has persisted to the point that most forward-thinking doctors recommend testing your levels annually.

And for nearly everyone over 30, supplementation is indicated. However, as a functional medicine doctor (and a busy mother of three), I recommend my patients get their vitamin D levels checked more frequently and as early in their adult lives as possible. Why? Because optimal vitamin D levels are crucial to nearly every single bodily function, including successful conception―for men and women―and maintaining a healthy pregnancy. Plus, optimizing your vitamin D levels sooner rather than later can prevent a slew of modern chronic ailments from manifesting later in life.

Here is everything you need to know about vitamin D for health, conception, pregnancy, in prenatal vitamins, disease prevention, and beyond.

What is vitamin D?

While its name is slightly misleading, vitamin D is both a vitamin and a hormone essential for healthy bodily function. Often nicknamed "the sunshine vitamin," vitamin D mostly enters our bodies via the sun, which is absorbed by our skin and converted to a usable form by cholesterol. You can get some vitamin D from specific foods, but the majority comes from good old-fashioned sunshine.

While all nutrients play a crucial, symbiotic role in maintaining health, vitamin D is especially important as it is essential for nearly every single bodily system and function including the musculoskeletal, gastrointestinal, renal, endocrine, and cardiovascular systems.

It’s even essential for healthy genetics and gene expression. Vitamin D has been shown to be responsible for up to 3 percent of what’s known as "gene transcription," the process in which your inherited genes are expressed or activated. In other words, vitamin D plays one of the most essential roles in nourishing your body, protecting your genes, preventing acute and chronic disease, and maintaining your overall health.

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How vitamin D supercharges your health and prevents disease.

Vitamin D and fertility.

While the research on vitamin D, fertility, and conception is up-and-coming, the studies that have been done are promising. For example, it’s been shown that vitamin D supplementation can increase a couple's chances of conceiving when using IVF, and new research suggests vitamin D supplementation may increase fertility and sperm count in men.

Plus, given what we now know about how vitamin D levels affect your immunity, inflammatory levels, and overall health, I wager we’ll be seeing many more exciting studies published in the coming years. For now, it seems prudent for future fathers (that’s you, guys) to get serious about their vitamin D levels to enhance their chances of a speedy conception.

Vitamin D and pregnancy.

Vitamin D: Guide to Deficiency Symptoms, Foods, Benefits, and More

Photo: Vera Lair

Now that we’ve got dads on board with vitamin D optimization, it’s time to move on to the moms. While vitamin D optimization will benefit women at any time in their life, it’s absolutely essential you keep on top of your levels before getting pregnant (ideally) and definitely during and after pregnancy. Supplementing with other key nutrients like DHA, calcium, and folic acid can be helpful during pregnancy, too.

Significant evidence shows that vitamin D deficiency during pregnancy increases your risk of anemia, gestational diabetes, pre-eclampsia, bacterial vaginosis, and unplanned caesarean birth. For baby, a variety of studies have shown suboptimal vitamin D levels can negatively affect an unborn child’s health in a number of ways including lower birth weight, tooth enamel defects, lowered cognitive function, and increased risk of obesity.

If that isn’t enough to turn your head, studies show you can reduce your baby's risk of asthma by 40 percent by increasing your intake of vitamin D. Vitamin D also plays a key role in the nutritional quality of your breast milk. Therefore, if you’re supplementing for two, I tend to recommend a higher-dose supplementation for breastfeeding mothers, often 5,000 IUs daily and up. Talk to your doctor or health care practitioner about what’s best for you.

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Vitamin D and hormone and thyroid health.

The thyroid is one of the most powerful glands in your body, regulating everything from metabolism and body temperature to hormonal balance and sleep patterns. It’s also a key player in fertility, pregnancy, and postpartum recovery. Therefore, if you want to increase your chances of a healthy conception, pregnancy, and postpartum period, protecting your thyroid is key.

Beyond pregnancy, caring for your thyroid will help you maintain a healthy weight, mood, sleep cycle, immunity, and energy levels and keep your hair, skin, and nails youthful and strong. Vitamin D plays a crucial role in thyroid health as it regulates the production of thyroid hormones, which help protect you from thyroid diseases.

Further studies have shown low levels of vitamin D levels are associated with chronic thyroid conditions like autoimmune thyroid disease such as Hashimoto’s thyroiditis and Grave's disease. I mention this in the context of pregnancy, birth, and postpartum health because many of the patients I see with thyroid insufficiencies are mothers.

The reason is pregnancy, birth, and caring for a new baby require an increased amount of stress hormones, sleep deprivation, and stamina. This puts a huge strain on the body’s hormonal balance and nutrient reserves, which often results in a compromised thyroid and adrenals. Ladies, if I could give you one piece of preventive advice for a healthy postpartum recovery it would be to take care of your thyroid before, during, and after your pregnancy―and getting enough vitamin D is a great place to start.

Vitamin D and immunity.

While vitamin C and zinc have earned gold-standard status for boosting immunity and protecting against cold and flu, the truth is, getting enough vitamin D is just as important.

Optimal vitamin D levels have been shown to positively affect the innate and adaptive immune system in a variety of ways including boosting genetic expression of white blood cells during winter months, helping the immune system adapt and ward off infection, reducing inflammation, and reducing the chance of upper respiratory infections.

Vitamin D deficiency has also been associated with a variety of autoimmune diseases including multiple sclerosis, lupus, diabetes, rheumatoid arthritis, and thyroid diseases such as Hashimoto’s and Grave’s disease. And this is just a small sampling of the research linking optimal vitamin D levels with improved immunity.

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Vitamin D and cancer.

When it comes to cancer, recent findings on epigenetics and the slow growth rate of many cancers, it’s a comfort to know we wield enormous power in our ability to prevent a worst-case scenario. Optimizing your vitamin D levels is one simple, affordable, and incredibly effective way to go about this.

Vitamin D insufficiency is commonplace in many types of cancer, most notably breast, prostate, lung, thyroid, and colorectal cancer; with 77 percent of patients either deficient or with suboptimal levels. And the lower their levels, the more aggressive the cancer. Optimal vitamin D levels have also been shown to affect cancer outcomes by decreasing mortality rates.

Vitamin D and inflammation.

Inflammation is now recognized as a causal factor in nearly every chronic condition―from heart disease and depression to cancer.

As a functional medicine physician, I can tell you, it’s no exaggeration to say inflammation has become a worldwide epidemic. The good news is there is plenty we can do to keep our inflammatory levels in check, including eating a balanced diet with plenty of fruits and vegetables, reducing stress, limiting our intake of processed foods, exercising, getting enough sleep, and getting enough anti-inflammatory vitamin D.

How does vitamin D help inflammation? It works by modulating the release and proliferation of cytokines―chemical messengers that initiate inflammation. And while some inflammation can be a good thing―like the protective swelling that occurs after a physical trauma―chronic inflammation is problematic as it causes body breakdown.

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Vitamin D and gut health.

While probiotics are all the rage in promoting good gut health, vitamin D has been shown to play a crucial role in restoring beneficial gut bacteria, which, in turn, has a positive effect on metabolism. Further, a variety of studies have shown vitamin D plays a key role in the health of the gut mucosal lining, acting as an anti-inflammatory, anti-infective, and immune booster to protect against viruses and other pathogens.

Vitamin D and bone health.

You've probably heard vitamin D is good for your bones, but why? Vitamin D prevents the breakdown of bones because it is crucial for the absorption of calcium, the structural element of bones. In the small intestines, vitamin D works to shuttle the calcium we consume from food into the blood stream. Maintaining adequate calcium and vitamin D levels throughout life, as part of a well-balanced diet, may reduce the risk of osteoporosis.

To boost vitamin D's calcium absorbing powers, try adding vitamin K2 to your diet or supplement routine. Vitamin K2 acts as an essential "GPS" for the calcium liberated by vitamin D, ensuring it gets to the right places in your body―like your bones―while staying out of the wrong places―like your arteries. Vitamin K2 is a must for safe vitamin D supplementation.

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Labs to request for vitamin D deficiency.

The safest and smartest way to optimize your vitamin D consumption is to monitor your blood levels. To do so, have your doctor specifically order a 25-hydroxy vitamin D test, also known as the 25-OH D test. The optimal (not just "normal") amount you want to see is 45 to 65 ng/mL, and in some cases, even higher levels are appropriate.

How to get more vitamin D.

Vitamin D: Guide to Deficiency Symptoms, Foods, Benefits, and More


The amount of vitamin D required to replenish deficiencies depends upon your lab tests, so check with your provider for individual recommendations and follow these guidelines: Get enough unfiltered, unprotected sunlight each day (see below). Your body absorbs vitamin D from the sun, so it is crucial to get outside and soak it up. If you cannot get outside every day, you live in a more northern region, or your vitamin D levels are low, you may need to supplement. I suggest choosing a vitamin D3 supplement with vitamin K2, and work closely with your doctor to monitor your levels.

Sources of whole vitamin D-boosting foods include:

Vitamin D and sun exposure.

There are many healing benefits of the sun, but is there a right way to get vitamin D, especially in the summer? In my experience as a physician and based on the current research, moderate sun exposure is best. Therefore, I recommend getting some unprotected sun exposure every day based on the Vitamin D Council’s recommendations for your skin type, location, etc. (see below), and to never let your skin burn. Then be sure and protect yourself with a nontoxic sunscreen thereafter.

Be aware that in more northern latitudes sun exposure may not be strong enough to stimulate vitamin D production in the winter. If you live in these locations you might want to consider implementing a winter supplement routine.

Here are the Vitamin D Council’s sun exposure guidelines based on skin type:

  • Those with very light to light skin likely need 10 to 15 minutes of unprotected sun exposure.
  • Those with naturally tan skin can take unprotected sun for 15 to 20 minutes.
  • While those with darker skin can safely take one to two hours of unprotected sun exposure.

To recap:

  • Most of us who live in North America are at high risk of vitamin D deficiency.
  • The 25-hydroxy vitamin D test, also known as the 25-OH D test, is the best way to determine your vitamin D levels.
  • Vitamin D is both a vitamin and a hormone essential for nearly every single bodily function.
  • Optimal/functional ranges lie between 45 and 60 ng/mL, and higher levels may be appropriate for some individuals.
  • Vitamin D deficiency has been associated with a wide variety of conditions including autoimmune diseases, chronic inflammatory conditions (like heart disease, metabolic syndrome, and MS), cancer, gut health, thyroid conditions, fertility (in men and women), pregnancy complications, and developmental issues in children.
  • Vitamin D is especially important for new mothers during preconception, conception, pregnancy, and postpartum.
  • Your best source of vitamin D is the sun. But be careful about overexposure.
  • Your next best source is a D3/K2 supplement, as recommended by your doctor or health care practitioner.
  • You can also get vitamin D from foods such as mushrooms, mackerel, sockeye salmon, cod liver oil, grass-fed beef, sardines, and eggs.
  • As a functional medicine doctor, I recommend getting your levels checked at least twice annually, possibly more if you’re on a high-dose supplementation protocol.

Ready to learn how to fight inflammation and address autoimmune disease through the power of food? Join our 5-Day Inflammation Video Summit with mindbodygreen’s top doctors.

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