Featured in: The Top 10 Brain Supplements

Before we go into the side effects of low Vitamin D, I want to go over some basics. Vitamin D3, as it is more formally known, affects some 1,000 genes and every cell in our bodies. These genes and cells turn on certain functions in our bodies, such as bone metabolism, suppressing tumor formation and cognitive function. It’s also considered a ‘prohormone‘. 

Vitamin D helps moderate immune function and inflammation and interacts with hormones like testosterone, human growth hormone, and estrogen. Pretty impressive for one little vitamin. And one we can manufacture it ourselves with the right building blocks. As you can probably start to imagine, the side effects of low Vitamin D are far-reaching. 

It is estimated that 1 billion people worldwide have Vitamin D deficiency and in the US, 41.6% of adults. It’s 69.2% of Hispanics and 82.1% of African-Americans (Healthline, 2018)! Those are some big numbers that we can’t ignore. It is confirmed that the darker the color of skin someone has, the harder it is to get Vitamin D from the sun (Asprey, 2017). Even lighter skin people who use sunscreen are blocking out Vitamin D along with the rays.

We’ll go over where we can get Vitamin D naturally, the best test for it and some side effects from lack of Vitamin D in our body. Then we can talk about solutions.Hand holding Vitamin D capsule

We can get Vitamin D from the sun and a few foods but most people don’t get enough. 

Where We Get It Naturally

As you probably know, we get Vitamin D from the sun. Also from fatty fish and from Vitamin D fortified dairy products. Our bodies manufacture pre-vitamin D3 we get from the sun and foods. However, we only get small amounts from food for this process. Almost always not enough.

After a chemical process in the liver, and then the kidneys, it then binds with a protein and travels to the near and far reaches of our bodies. Then, other cells in the body turn it into actual Vitamin D, which is actually a prohormone. In this form, it’s called calcitriol and this is what does the magic in our bodies (Jeon and Shin, 2018). 

Testing for Vitamin D 

When we are measured for Vitamin D levels in the body, they are actually measuring either the pre-activated Vitamin D or sometimes the activated Vitamin D. The Vitamin D Council (2019) believes the accurate level to test our Vitamin D on is the pre-activated Vitamin D, [25(OH)D]. The Vitamin D Council says this is the only one that will tell you whether you’re getting enough Vitamin D.

Per The Vitamin D Council, 40-80 ng/ml is optimal. Per Dale Bredesen, M.D., 50-80 ng/ml is optimal of 25(OH)D.

What Are the Side Effects of Low Vitamin D?


Low Vitamin D has been linked to depression, especially in older adults (Spritzler, 2018). There are studies that say it is not, but those used low dosages of Vitamin D as a control so really ended up being inconclusive.

However, researchers have found that a high percentage of people with depression have low Vitamin D levels. The graduate students referenced below, Vellekatt and Menon, reviewed multiple studies regarding the treatment of depression with Vitamin D and found that it conclusively does help depression. They did note that it might be the antioxidant properties of Vitamin D that made the difference. 

Depression and Fatigue are signs of low Vitamin D 

Tiredness and Fatigue 

There are many causes of tiredness and fatigue, but don’t overlook low Vitamin D as a culprit. Now that you’ve read about the far-reaching functions of Vitamin D, it makes sense that if you’re low, your cells may not be getting what they need to keep you going. Many studies have found that people with chronic fatigue often have low Vitamin D blood levels.  

Getting Sick or Infections Often 

Since one of Vitamin D’s functions (and one of the most important) is keeping our immune systems strong, being low leaves us open to more infections and illnesses. Vitamin D works directly with the cells that fight infection (Spritzler, 2018). 

Studies show a link between low Vitamin D levels and respiratory tract infections. Dave Asprey (2017) noted he got sick much less often after beginning supplementation of Vitamin D. 

Vitamin D is also related to cancer prevention and even has been shown to reduce tumor size with certain cancers.


bone loss causes fractures


Bone Loss

We need Vitamin D in order to absorb calcium. People with bone loss, primarily older people, are often low on Vitamin D too. Anytime we are supplementing calcium in our diet, we should be taking Vitamin D as well to help absorb the calcium. A research study of 1,100 middle-aged women in menopause or postmenopause, found that low bone mineral density was linked to low Vitamin D levels (Spritzler, 2018). Taking adequate Vitamin D will help prevent bone loss and reduce the risk of fracture. 

Hair Loss

Hair loss in women is associated with low Vitamin D levels, especially with the auto-immune disease alopecia areata. Stress could be a factor in lesser hair loss too. But in studying women with hair loss, most had low blood Vitamin D levels. There could be other causes too, of course, so check with your doctor.

 – Bone, Back, and Muscle Pain

Apparently, bone and lower back pain is an indicator of low Vitamin D. Researchers have found a connection between Vitamin D levels and back pain in more than 9,000 older women, according to one study. Those with the deficiency were more likely to have back pain, sometimes severe enough to limit daily activities.

Several studies have been done regarding Vitamin D and muscle pain too. It was found that when Vitamin D levels were normal, people experience less pain than people who are low. A nerve cell called nociceptors, which senses pain, has a Vitamin D receptor. Many people with chronic pain are low in Vitamin D. Interesting correlation.

Dr Axe Video on Vitamin D Deficiency:


Where We Are Now

Some feel Vitamin D is the most important supplement we can take. Especially since so many people are deficient. Since it works in virtually every cell in the body, allowing for their various functions, it’s critical for health that we have enough to run on.

Dale Bredesen states in his book, The End of Alzheimer’s, that lowered Vitamin D levels are associated with cognitive decline. Moreover, some of the genes mentioned earlier are in the brain and responsible for creating and maintaining brain synapses. If Vitamin D levels aren’t optimal, the wrong genes could be activated, causing the wrong activities in the brain.

Many recommend taking 1,000 IU for every 25 pounds of body weight.

For your reference, magnesium and Vitamin D work synergistically. See the related article on Magnesium.

I hope you became aware of how important Vitamin D3 is for you and are ready to add some Vitamin D3 to your supplement list. Click on the link below to get started boosting your brain, body, and your immune system today. 

Thank you for visiting! Please leave any questions, comments or experience in the Comments section below.


Asprey, D. (2017). eBook. The Bulletproof Diet. Published by Rodale Wellness.

Bredesen, D. (2017). Book. The End of Alzheimer’s. Published by Avery, An Imprint of Penguin Random House LLC.

Jeon, S. and Shin, E. (2018). NCBI. US National Library of Medicine, National Institutes of Health. Exploring vitamin D metabolism and function in cancer. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5938036/

Spritzler, F. (2018). Healthline. 8 Signs and Symptoms of Vitamin D Deficiency. https://www.healthline.com/nutrition/vitamin-d-deficiency-symptoms

Vellekkatt, F. and Menon, V. (2019) NCBI. US National Library of Medicine, National Institutes of Health. Efficacy of vitamin D supplementation in major depression: A meta-analysis of randomized controlled trials. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6515787/

Vitamin D Council (2019). The physiology of vitamin D. https://www.vitamindcouncil.org/the-physiology-of-vitamin-d/#.XY_sYEZKiM8

Get Updates!

Sign up for email notifications when there are new articles on MyWellBrain!