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Vitamin D

September 2020

What is vitamin D?

Vitamin D, also known as calciferol, is a fat-soluble vitamin that is naturally present in very few foods, added to some foods, and available as a dietary supplement. When our skin is exposed to UV light, our body begins to make vitamin D.

What are the sources of vitamin D?

Sunlight – Being in the sun for 15-20 minutes 3 times a week is usually sufficient for most people.

Food - Vitamin D is found naturally in very few foods, so certain foods have been fortified with vitamin D. Examples of vitamin D containing foods are salmon, mackerel, sardines, fortified milk, and fortified cereal.

• Dietary Supplements

Image: https://www.diabetes.co.uk/food/vitamin-d.html

Why is vitamin D important?

• Absorbing calcium - Our bodies can only absorb calcium when vitamin D is present. If our bones aren’t healthy, then certain conditions can arise. Children could develop rickets causing bones to be soft and weak, and adults could develop a similar disorder of soft bones called osteomalacia.

• Keeping bones strong - Our bones are made up primarily of calcium, which as stated above needs vitamin D for absorption.

• Working with parathyroid glands - Our parathyroid glands work to keep calcium in the proper balance in our bodies. When there is sufficient calcium in the diet and sufficient active Vitamin D, dietary calcium is absorbed and put to good use throughout the body. If calcium intake is insufficient, or vitamin D is low, the parathyroid glands will ‘borrow’ calcium from the skeleton in order to keep the blood calcium in the normal range.

What factors could affect vitamin D levels?

Where you live – People living in northern regions are at a higher risk for vitamin D deficiency during the winter months because their skin may not be able to produce any vitamin D from sun exposure.

Age – Skin’s ability to produce vitamin D decreases as we age. For example, if you are over the age of 65, then you generate only one-fourth as much vitamin D as you did in your 20’s.

Skin color – People with darker skin typically have lower levels of vitamin D than lighter-skinned people. More sun exposure is necessary for people with darker skin tones to synthesize a sufficient amount of vitamin D.

Weight – Vitamin D is a fat-soluble vitamin, meaning that it is stored in fat cells. In people with obesity, vitamin D is stored in the fat and less is circulating through the blood.

Diet – Since vitamin D is very important for our bodies to function properly but is not found in many foods, the US. government started the milk fortification program in the 1930s to combat rickets, a major health problem at the time. Other foods have become fortified like cereal and orange juice.

Certain health conditions – People with conditions such as inflammatory bowel disease, liver disease, or cystic fibrosis, among others, may have trouble absorbing vitamin D, which can lead to deficiencies.

How much vitamin D do I need?

Recommended dietary allowance (IU/day)
Upper level intake (IU/day)

0-6 months

400 IU

1000 IU

6-12 months

400 IU

1500 IU

1-3 years

600 IU

2500 IU

4-8 years

600 IU

3000 IU

9-70 years

600 IU

4000 IU

>70 years

800 IU

4000 IU

Females 14-50 years old, pregnant/lactating

600 IU

4000 IU

*According to the American Journal of Clinical Nutrition, the upper limit of 4000 IU/day is too conservative as newer research suggests that the upper limit be changed to 10,000 IU/day.

What conditions can vitamin D help?

Bone health and osteoporosis – Vitamin D and calcium supplements Can help slow bone mineral loss, which helps prevent fractures and osteoporosis.

Testosterone levels – Recent research have found that there may be a link between low testosterone levels and low vitamin D levels.

Immune Health – Vitamin D plays a role in our immunity and immune response. Vitamin D deficiency is associated with increased autoimmunity and increased

susceptibility to infection.

Multiple Sclerosis – Research suggests that long-term use of vitamin D supplements may reduce the risk of multiple sclerosis.

Psoriasis – When applied topically, vitamin D or using calcipotriene (vitamin D compound available with a prescription) can treat the plaques associated with psoriasis in certain people.

Cognitive health – Early research suggests that vitamin D might play a role in our cognitive functioning.

Cancer – Research suggests that taking vitamin D and calcium might help prevent certain cancers

When adding any new vitamin or supplement to your regimen, please consult your doctor or pharmacist first.

What medications can interact with vitamin D supplements?

• Aluminum

• Laxatives

• Steroids (ex: prednisone)

• Cholesterol-lowering drugs (ex: cholestyramine and colestipol)

• Seizure-control drugs (ex: phenobarbital and phenytoin)

• Rifampin

• Orlistat

• Digoxin (Lanoxin)

• Diltiazem (Cardizem, Tiazac)

• Thiazide diuretics (ex: HCTZ)

If you are worried about any drug interactions, contact your pharmacist.

Vitamin D Deficiency

What is vitamin D deficiency?

Vitamin D deficiency means that there is not enough vitamin D in the body.

What causes vitamin D deficiency?

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

Weight loss surgeries — Weight loss surgeries that reduce the size of the stomach and/or bypasses part of the small intestines make it very difficult to consume

sufficient quantities of certain nutrients, vitamins, and minerals. These individuals need to be carefully monitored by their doctors and need to continue

to take vitamin D and other supplements throughout their lives.

Obesity – A body mass index (BMI) of over 30 has been associated with lower levels of vitamin D. Since vitamin D is fat-soluble, it remains in the fat cells and less vitamin D is circulating in the body. Obesity often makes it necessary to take larger doses of vitamin D supplements to reach and maintain normal levels.

What other factors can lead to vitamin D deficiency?

Age – The skin’s ability to make vitamin D decreases as we age.

Mobility – People who are homebound or rarely outside 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. Often infant formulas also only include a small amount of D also. Therefore infants are at risk of not receiving enough vitamin D. This is

especially true for infants who are only fed breast milk.

What are the signs and symptoms of vitamin D deficiency?


Severe vitamin D deficiency in children causes rickets, which is very rare. Rickets shows up as incorrect growth patterns, weakness in muscles,

pain in bones, and joint deformities. Children with a vitamin D

deficiency can present with weakness or sore and painful muscles.


A lack of vitamin D is not as obvious in adults. Signs and symptoms include:

• Fatigue

• Bone pain

• Muscle weakness, muscle cramps, or muscle aches

• Mood changes, like depression.

Can I take too much vitamin D?

Yes. Taking too much vitamin D can lead to a buildup in the body leading to toxicity. It is very rare and usually occurs over time. This toxicity typically occurs when someone is taking 40,000-100,000IU per day over months. It can lead to hypercalcemia, a condition in which too much calcium builds up in the blood, potentially forming deposits in the arteries or soft tissues. It may also predispose women to painful kidney stones. A 2010 study published in the Journal of American Medical Association showed that intake of very high doses of vitamin D in older women was associated with more falls and fractures.