Vitamin D is an essential vitamin that many don’t put enough importance on taking. The reality is that putting more emphasis on taking this vitamin is vital. The reason why it's so important is that it decreases the risk of experiencing health conditions such as diabetes, cancer, heart disease, and more. Many people don’t realize they’re deficient in vitamin D. Not only does a lack of vitamin D result in developing health conditions, but it makes it more challenging for a person on a diet to achieve their goals. Why is that? Well, without vitamin D, it’s easier to gain weight, which can be counterproductive when applying a new diet. However, get enough vitamin D, and going on the keto diet, a high, low carb diet discussed in the Body Reboot book and achieving health goals will be a lot easier. 

Dr. Axe explains what vitamin D is and why your body must absorb it. This vitamin is different than other vitamins, however, because it gets absorbed from the sun as opposed through food sources. 

Vitamin D is a fat-soluble vitamin that’s stored in the liver and fatty tissues. This means that increased body fat has the ability to absorb this vitamin and keep it from being used within the body.

It’s somewhat different than other vitamins because the body makes most of it on its own, rather than solely relying on food sources.

What Does It Do in the Body?

Here’s an easy breakdown of how this vitamin is made and what it does in the body:

The body converts sunshine into chemicals that are then used by the body. In particular, when UV-B sunshine rays land on the skin  a substance in the skin called 7-dehydrocholesterol is literally converted into vitamin D3.

7-dehydrocholesterol or the cholesterol in our skin — which is very similar to cholesterol itself — converts “previtamin D” and makes it into usable D3, which is sometimes also called provitamin D.

Previtamin D first travels through the kidneys and liver in the bloodstream and then is converted into a biologically active and usable substance called calcitriol.

Vitamin D actually becomes a hormone within the body, particularly a secosteroid hormone. What we know as vitamin D is really a precursor to a steroid hormone.

Research indicates that it impacts not only the skeletal structure, but also blood pressure, immunity, mood, brain function and ability to protect ourselves from cancer.

Many people assume that the best way to acquire vitamin D is through drinking milk, eating fish or even taking supplements like cod liver oil. While these do serve as food sources, direct exposure to the sun is actually the best way to absorb this important vitamin.

When you sit in the sun unexposed, without sunscreen, for roughly 10 minutes, you likely absorb about 10,000 units of natural vitamin D. However, keep in mind that this amount differs from person to person, depending on skin tone.

Melanin is a substance that affects how light or dark your skin color is, and the more melanin you have in your body, the darker your skin color will be. Melanin gets released when we are exposed to the ultraviolet rays of sunshine.

The more sunshine we receive, the more melanin is released in our skin. It’s believed that up to 90 percent to 95 percent of most people’s vitamin D comes from casual sunlight exposure.

The amount of melanin you have in your skin affects the amount of D vitamin you can produce, so the fairer your skin, the more easily you can make it.

The cholesterol in the skin converts melanin into usable vitamin D to be distributed throughout the body. This is why, for many people, a slight to moderate rise in cholesterol levels can be experienced in the winter months when there is less exposure to sunshine, since it’s common to spend much more time indoors.

Cleveland Clinic also reveals various medical conditions that a lack of vitamin D can cause. As we mentioned earlier, not having enough vitamin D can lead to obesity. That's why it's vital to make sure you’re getting enough of this vitamin. 

Are there medical conditions that can cause a vitamin D deficiency (shortage)?

Yes. Vitamin D deficiency can be caused by specific medical conditions, such as:

Kidney and liver diseases. These diseases reduce the amount of an enzyme needed to change vitamin D to a form that is used in the body. Lack of this enzyme leads to an inadequate level of vitamin D in the body.

Cystic fibrosis, Crohn's disease, and celiac disease. These diseases do not allow the intestines to absorb enough vitamin D.

Gastric bypass surgery. This weight-loss surgery removes part of the stomach and/or the intestines. Reducing the size of these organs lowers the amount of vitamin D-containing nutrients that can be absorbed.

Obesity. A body mass index greater than 30 is associated with lower vitamin D levels. It is thought that the fat actually holds onto the vitamin D, and does not allow it to be released into the bloodstream.

Other factors that can lead to vitamin D deficiency:

Age. The skin's ability to make vitamin D lessens with age.

Mobility. People who are homebound or are rarely outside (e.g., in nursing homes and other facilities) are not able to use sun exposure as a source of vitamin D.

Skin color. Dark-colored skin is less able to make vitamin D than fair-colored skin.

Human breast milk. A woman's breast milk only contains a small amount of vitamin D. Infant formulas often do, too. Therefore infants, particularly those who are breastfed exclusively, are at risk for not receiving enough vitamin D.

If you’re wondering what the benefits of vitamin D is, Huffington Post does an excellent job explaining. They also discuss why you should be taking this vitamin. Not everyone absorbs vitamin D the same way, and .oftentimes the body doesn’t have enough of it. 

Over the years many studies have shown low Vitamin D may lead to heart disease, diabetes, dementia, aggressive prostate cancer and Alzheimers. A new study published in The Journal of Clinical Endocrinology Metabolism explored the importance of vitamin D related to heart health. A connection was made between children having low vitamin D levels and experiencing heart disease later in life. Learn more on this connection between heart disease and low vitamin D.

Benefits of Vitamin D

Vitamin D helps build up calcium in your body which strengthens bone and teeth health

Decreased risk of osteoporosis, diabetes, dementia and some cancers including breast, colon, prostate, ovarian, esophageal and lymphatic

Helps lower blood pressure levels and hypertension

Regulates your immune system for optimal efficiency and fighting disease

Studies have shown that it can decrease multiple sclerosis in women

Vitamin D is arguably the most important vitamin you could take. Vitamin D is actually a hormone; it's not even a vitamin and it affects our entire body. Whenever, you feel fatigued or have low energy – it's quite possible your Vitamin D levels are low. A vitamin D deficiency occurs when the level of vitamin D in your body is too low. Vitamin D helps the body use calcium from our diet which is essential for us as humans to maintain bone strength. If you feel you might be experiencing symptoms of a vitamin D deficiency, it is important to get tested and treated because it can eventually cause your bones to become thin, brittle or mis-shapen.

Science Daily also discusses the importance of vitamin D and precisely how it promotes healthy bones: 

Vitamin D has long been known to promote healthy bones by regulating calcium levels in the body. Lack of sufficient vitamin D in very young children results in rickets, which can be easily prevented by vitamin D supplements. Only recently the scientific community has become aware of a much broader role for vitamin D. For example, we now know that, in addition to its role in maintaining bone health, vitamin D is involved in differentiation of tissues during development and in proper functioning of the immune system.

In fact, over 900 different genes are now known to be able to bind the vitamin D receptor, through which vitamin D mediates its effects. In addition to protecting against rickets, evidence now strongly indicates that a plentiful supply of vitamin D helps to protect against bone fractures in the elderly. Evidence also continues to accumulate suggesting a beneficial role for vitamin D in protecting against autoimmune diseases, including multiple sclerosis and type I diabetes, as well as some forms of cancer, particularly colorectal and breast.

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Sources: Dr. Axe, Cleveland Clinic, Huffington Post, Science Daily