Vitamin D Deficiency: Know the Signs and Symptoms

If you spend most of your time indoors or live in regions of the Northern Hemisphere, you may be at a greater risk of vitamin D deficiency. Even with adequate sun exposure and a varied diet, vitamin D deficiency is very common and affects over 40% of people in North America. (6)(17) Keep reading to learn how to prevent deficiency, identify the signs of vitamin D deficiency, and find out if you might be at risk.

What is vitamin D?

Vitamin D is a fat-soluble vitamin that can be absorbed in the small intestine along with dietary fats and stored in the liver and body’s fat tissues for long-term use. (17) It’s also one of the few vitamins the body can make on its own. Vitamin D helps the body absorb and regulate calcium levels in the blood, which is especially important for maintaining strong, healthy bones. Beyond bone health, vitamin D supports immune, heart, and cognitive function. (17)(19)

Vitamin D sources

Vitamin D comes from three main sources, including sun exposure, diet, and supplements.

Sun exposure

UVB rays from the sun react with a cholesterol precursor in the skin, where 7-dehydrocholesterol is converted to cholecalciferol, also known as vitamin D3. The liver and kidneys are then responsible for converting cholecalciferol to calcitriol, the active form of vitamin D3. (17)

Diet

Vitamin D is primarily found in animal-derived foods, including beef liver, cheese, eggs, and fatty fish. (17) Certain mushrooms, such as maitake and UV-treated portabella, also contain small amounts of vitamin D. (16) Some foods, including breakfast cereals, dairy products, non-dairy beverages (e.g., almond and soy milk), and orange juice, may be fortified with vitamin D. (15)

Supplements

Vitamin D is also available in supplement form and may be necessary if you’re not getting enough through diet and regular sun exposure. There are two forms of vitamin D in food and supplements, D2 (ergocalciferol) and D3 (cholecalciferol). Both can help you meet your daily vitamin D needs; however, D3 has been shown to be better absorbed by the body. D2 is often less expensive to produce than D3 and, therefore, frequently added to fortified foods. (15)

Most vitamin D supplements are derived from lanolin, a waxy substance secreted from the sweat glands of sheep. (20) An alternative source is lichen, derived from a combination of fungus and algae, making it a suitable alternative for individuals following a strictly plant-based diet. (20)(3)

Did you know?
Five to 30 minutes of sun exposure, without sunscreen, a couple of times per week is sufficient for most people to produce enough vitamin D. (13)

Regions prone to vitamin D deficiency

People living in regions of the Northern Hemisphere are at greater risk of developing a vitamin D deficiency. (17)

What is vitamin D deficiency, and what are the signs?

Low vitamin D status can occur in individuals who do not spend enough time in the sun or don’t consume enough vitamin D through their diets. Vitamin D deficiency symptoms include bone and muscle pain, chronic fatigue, hair loss, and general weakness. (10)(1)

Deficiency is directly linked to several health concerns, including osteoporosis, heart disease, cancer, and impaired immune function. (17) A simple blood test can help determine whether you have vitamin D deficiency. Consult your healthcare practitioner for testing and an appropriate treatment plan if necessary.

Vitamin D deficiency can be determined by a simple blood test. This table shows vitamin D status and corresponding blood levels for children and adults. (18)

Vitamin D deficiency risk factors

Certain populations are at an increased risk of vitamin D deficiency. At-risk individuals may need to be especially conscious about consuming vitamin D-rich foods, spending more time in the sun, or adding a supplement when advised by a practitioner. (17)

Breastfed infants

The amount of vitamin D in breast milk is related to the mother’s vitamin D status. While breast milk is a very nutritious choice for babies, it only has small amounts of vitamin D (about 4 to 40 IU per liter). For this reason, breastfed babies may need to receive a daily supplement after birth until they get enough from their diet. (15)

Certain health conditions

Since vitamin D is a fat-soluble vitamin, its absorption depends on the gut’s ability to absorb fat. Conditions that cause fat malabsorption, such as celiac disease, Crohn’s disease, and ulcerative colitis, can increase the risk of vitamin D deficiency. (15)

Darker skin tone

Greater amounts of the pigment, melanin, result in darker skin color and decrease the skin’s ability to produce vitamin D from sunlight. (15) The highest incidence of vitamin D deficiency is seen in individuals of African American (82%) and Hispanic descent (69%). (6)

Limited sun exposure

People who spend much of their time indoors or live in northern regions of the world may not get enough sunlight exposure to produce sufficient vitamin D, especially in the winter months. (22)

Obesity

Individuals with a body mass index (BMI) of 30 or greater are more likely to have low levels of vitamin D. The skin is able to synthesize vitamin D, however, greater amounts of subcutaneous fat stores the vitamin D and reduces the amount released into circulation. (15)

Vegans and vegetarians

Because vitamin D is primarily found in animal and animal-derived foods, vegans and vegetarians may struggle to get enough vitamin D through diet alone. (11)

Health effects of vitamin D deficiency

Outlined below are some of the negative health effects of vitamin D deficiency.

Altered immune function

The immune system, which is the body’s primary defense against foreign invaders, is enhanced by vitamin D. Without adequate vitamin D, immune cells (e.g., macrophages, B-cells, and T-cells) can’t properly fight off infection. (5) Research has determined that individuals with vitamin D deficiency are more likely to contract upper respiratory tract infections, such as the common cold or seasonal flu, compared to individuals with normal vitamin D status. (2) Low vitamin D levels are also associated with an increased incidence of certain autoimmune diseases, conditions in which the body misidentifies its own cells as invaders. (2)

Increased risk of cardiovascular disease

Vitamin D deficiency is associated with an increased risk of cardiovascular disease and heart failure. Other cardiovascular disease risk factors that are also influenced by low vitamin D status include high blood pressure, type 2 diabetes, high BMI (≥30), and high triglyceride levels. (9)

Increased risk of Alzheimer’s disease and dementia

Low vitamin D status is related to an increased risk of neurodegenerative disease, including Alzheimer’s disease and dementia. This relationship is positively correlated; the risk of developing Alzheimer’s disease increases as the severity of vitamin D deficiency increases. (9)

Increased risk of cancer

Certain cancers, including breast, colorectal, and prostate cancer, may be linked to vitamin D deficiency. (7) Deficiency may contribute to tumor growth and metastasis in breast cancer. (23) When comparing levels of vitamin D and colon cancer risk, levels less than 12 ng/mL increased risk by 31% in comparison to levels of at least 20 ng/mL. (12) Another study suggests a link between vitamin D deficiency and aggressive forms of prostate cancer in African-American and European-American men. (14)

Weakened bones

When vitamin D levels are low, calcium is pulled from the bones to maintain blood calcium homeostasis (balance). Vitamin D deficiency in children can lead to a condition called rickets, characterized by softened bones and bowed legs. Additionally, vitamin D deficiency can cause osteomalacia and osteoporosis in adults, making bones more vulnerable to fracture. (21)

Vitamin D deficiency can lead to osteoporosis, a condition characterized by weak, porous bones that are prone to fracture.

How to prevent and address vitamin D deficiency

Vitamin D deficiency may be prevented by getting adequate sun exposure and eating a varied diet with vitamin D-rich foods. (8)

Treatment for vitamin D deficiency depends on the severity of your condition. After determining your vitamin D status through a blood test, your healthcare practitioner will determine a proper treatment plan. Supplementation is most commonly used to treat vitamin D deficiency. Regular blood tests may be necessary to monitor your serum vitamin D levels, and your treatment plan may adjust accordingly. (10)

Since vitamin D is a fat-soluble vitamin and is stored in the body, supplementing with too much vitamin D can lead to toxicity. Consult your practitioner prior to supplementing for appropriate dosage instructions. (10)

The bottom line

If left untreated, vitamin D deficiency can have detrimental health effects. Although vitamin D deficiency is common, vitamin D status can be restored through supplementation, diet, and adequate sun exposure.