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We have all heard tidbits of information about the importance of Vitamin D from doctors, nutritionists, dieticians, friends, family, etc. In fact, you may have been told that we, as “Missoulians”, need extra Vitamin D due to the lack of sunshine we receive. Why exactly do we need Vitamin D? In addition to the health benefits, I would like to expose you to some additional facts of which you might not be aware. First, let’s briefly discuss vitamins.

A Brief Introduction to Vitamins1

Vitamins are essential micronutrients that play a variety of roles throughout the human body. There are two kinds of vitamins: fat-soluble and water-soluble. Watersoluble vitamins (B complex and C) need replenishing more frequently as they are degraded within the fluids in your body. Fat-soluble vitamins (A,D,E, & K) do not need replenishing as quickly due to the fact that they are stored in the liver and adipose (fatty) tissues when they are not being utilized by your body. Power of Vitamin D

What Is Vitamin D and Why Do We Need It?2

Vitamin D plays a critical role in the body’s use of calcium and phosphorous. It works by increasing the amount of calcium absorbed from the small intestine, helping to form and maintain bone structure. Vitamin D also plays a role in our immunity. We all need adequate amounts of vitamin D to develop and to maintain strong bones and healthy teeth so as to avoid fractures and injury.

Surprisingly, there is research to suggest that bone turnover in the presence of osteoporosis/osteopenia also correlates with idiopathic Benign Paroxysmal Positional Vertigo (BPPV)3,4which is when crystals in your ear move causing you to experience a sensation of spinning or dizziness when you change positions. This means that if you have osteoporosis or osteopenia, your chances of experiencing positional vertigo may be higher as compared to someone who does not have it.

You may be thinking, “Yeah, yeah, it’s important for my bones.” Don’t stop reading yet! What if I told you that it can also help with balance and even more importantly, help you to avoid a fall. Another important function of Vitamin D is its role in muscular contractions. 5

In our bodies we have two different kinds of muscle fibers, type I (slow twitch) and type II (fast twitch). Simply speaking, slow twitch fibers are used for long duration activities such as running a marathon and fast-twitch fibers are used for quick, immediate action such as a sprint and a long jump. Vitamin D works specifically to help the fast twitch fibers react and contract faster. Knowing that, please picture this: you are walking along an icy sidewalk and preparing to cross the street. You go to step off of the sidewalk, miscalculate the distance to the ground and begin to slip. Which muscle fiber would you want to contract as quickly as possible to keep you upright so as to avoid falling to the ground? Yes, the fast-twitch muscle fibers!

How Do You Get Vitamin D?2

Unfortunately, very few naturally occurring foods contain vitamin D. Most of the vitamin D in the American diet is received from fortified foods including milk, breakfast cereals, and some brands of orange juice, yogurt, and other food products. It is also found in the flesh of oily fish such as salmon, tuna, mackerel, herring and sardines as well as in cod liver oil. In addition to food sources, one of the purest forms of Vitamin D is obtained through our skin when it is made in response to sunlight. We have all been warned to wear sunscreen when outdoors to protect our skin but research suggests a daily dose of at least 15 minutes of sun exposure without protection (i.e. sunscreen)

How Much Do We Need?2

The Recommended Dietary Allowance (RDA) for Vitamin D varies for the different stages of life. It would be beneficial to ask your doctor, a dietician, or a nutritionist the amount that is appropriate for you individually and/or what adjustments are needed to make up for the lack of ultraviolet light we receive. As mentioned earlier, 10-15 minutes of exposure to ultraviolet light, without sunscreen on the hands, arms and face, is necessary for the body to produce the active form of Vitamin D. This can easily be obtained, twice per week, in the time spent walking your dogs or biking to work. Please remember to use sunscreen after the recommended 10-15 minutes to avoid skin damage.

Groups at Risk of Vitamin D Insufficiency1,2

The following groups of people may require extra vitamin D in the form of supplements or fortified foods:

Covered and protected skin: This includes those that do not regularly leave their homes (homebound), those that cover all of their skin with clothing while outside for religious reasons or ceremonial dress, and those that frequently wear sunscreen block most of the synthesis of vitamin D from sunlight.
Elderly: The elderly have a reduced ability to synthesize vitamin D upon exposure to sunlight. Additionally, they are more likely to stay indoors and wear sunscreen which blocks vitamin D synthesis. Often, their diet may lack adequate amounts of this vitamin.
Breast-fed infants: A mother’s milk only provides a small amount of vitamin D, which is related to the mother’s vitamin D status. Mothers who supplement their diet with Vitamin D generally have higher levels in their breast milk. Otherwise, breast-fed infants often benefit from a vitamin D supplement. Ask your pediatrician prior to starting vitamin D for your baby.
Individuals with Dark Skin: Unfortunately those with darker skin are not able to synthesize as much vitamin D from sun exposure as compared to light-skin individuals.
Diseases/Conditions that cause Fat Malabsorption: As discussed above, vitamin D is a fat-soluble vitamin which means that its absorption depends on our intestines ability to absorb dietary fat. Those who have difficulty absorbing dietary fat may require supplementation of vitamin D. Examples include: Inflammatory bowel disease (IBD), obesity, those who have undergone gastric bypass surgery, liver disease, cystic fibrosis, celiac disease and Crohn’s disease.

Important Isn’t It?!

Vitamin D is an important micronutrient that our bodies need for a variety of reasons discussed above. Living in this beautiful city that we call home, its availability in the purest form can often be limited. Again, please consult your primary care providers, nutritionists, and dieticians to assist you in identifying the amount that your individual body needs.


Kelsey Turner PT, DPT is a vestibular physical therapist
at Element Physical Therapy located in Missoula, Montana.


1. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2011. 2. Dietary Supplements: What you need to know (2011). NIH Clinical Center. http://ods.od.nih.gov/HealthInformation/DS_WhatYouNeedToKnow.aspx
3. Osteoporosis as a risk factor for the recurrence of benign paroxysmal positional vertigo. Yamanaka T, Shirota S, Sawai Y, Murai T, Fujita N, Hosoi H.Laryngoscope. 2013 Nov; 123(11):2813-6. Epub 2013 Apr 8. 4. Vitamin D deficiency and benign paroxysmal positioning vertigo. Büki B, Ecker M, Jünger H, Lundberg YW.Med Hypotheses. 2013 Feb; 80(2):201-4. Epub 2012 Dec 14. 5. Study protocol for prevention of falls: a randomized controlled trial of effects of vitamin D and exercise on falls prevention. Uusi-Rasi K, Kannus P, Karinkanta S, Pasanen M, Patil R, Lamberg-Allardt C, Sievänen H.BMC Geriatr. 2012 Mar 26; 12:12. Epub 2012 Mar 26.