Vitamin D Deficiency

Vitamin D deficiency is a widespread condition affecting approximately 1 billion people worldwide, causing issues primarily with bones and muscles, yet many people don’t realize they have it because symptoms can be subtle or absent.

Table of contents

• What is Vitamin D Deficiency?
• Why Vitamin D is Important
• How Common is Vitamin D Deficiency?
• Signs and Symptoms
• Causes of Vitamin D Deficiency
• Who is at Higher Risk?
• How is it Diagnosed?
• Getting Enough Vitamin D
• Treatment
• Outlook

Hypovitaminosis D, Low Vitamin D

What is Vitamin D Deficiency?

Vitamin D deficiency means you don’t have enough vitamin D in your body. It primarily causes issues with your bones and muscles^[1]. Vitamin D is a fat-soluble vitamin (a vitamin that dissolves in fat and can be stored in the body) that is essential for normal bone development and maintenance^[1].

Vitamin D deficiency is often clinically silent, meaning many people have it without experiencing obvious symptoms^[3]. Doctors don’t routinely check vitamin D levels, so many people are deficient and don’t realize it^[4].

Why Vitamin D is Important

Vitamin D plays a crucial role in maintaining the balance of calcium in your blood and bones. Your body needs vitamin D so it can use calcium and phosphorus to build bones and support healthy tissues^[1]. When vitamin D levels are adequate, the body can properly absorb calcium from the diet^[4].

Without sufficient vitamin D, bones can become thin, brittle, or misshapen. Vitamin D deficiency prevents normal bone mineralization (the process by which minerals are deposited in bone tissue to make it strong)^[17]. In children, severe deficiency can result in rickets, a condition that causes bones to become soft and bend. In adults, it can lead to osteomalacia (soft bones) and osteoporosis (weak, brittle bones), increasing the risk of bone fractures^[1].

Vitamin D also plays important roles in your nervous system, musculoskeletal system, and immune system^[1]. It helps reduce inflammation and regulates processes such as cell growth, neuromuscular function, and immune function^[17].

With chronic or severe vitamin D deficiency, the decline in calcium and phosphorus absorption leads to hypocalcemia (low calcium levels in the blood). This causes secondary hyperparathyroidism, where the parathyroid glands become overactive trying to keep blood calcium levels normal. To balance calcium levels, your body takes calcium from your bones, which leads to accelerated bone breakdown^[1].

How Common is Vitamin D Deficiency?

Vitamin D deficiency is a common global issue. About 1 billion people worldwide have vitamin D deficiency, while 50% of the population has vitamin D insufficiency^[1]. The condition affects up to 1 billion people in both developed and developing countries^[3].

Approximately 35% of adults in the United States have vitamin D deficiency^[1]. According to the National Institutes of Health, almost 1 in 4 U.S. adults are considered low in vitamin D^[5].

Vitamin D deficiency is particularly prevalent among elderly people^[8]. It affects people of all ages, including infants, children, and adults^[1].

Signs and Symptoms

Most people with vitamin D deficiency are asymptomatic, meaning they have no symptoms^[5]. When symptoms do occur, they are often subtle or nonspecific, so the condition frequently goes unrecognized^[11].

In children, severe lack of vitamin D causes rickets. Symptoms of rickets include^[1]:

• Incorrect growth patterns due to bowed or bent bones
• Muscle weakness
• Bone pain
• Deformities in joints

Children with a mild vitamin deficiency may just have weak, sore, or painful muscles^[1].

In adults, symptoms of vitamin D deficiency might include^[1]:

• Fatigue or tiredness
• Bone pain or achiness
• Muscle weakness, muscle aches, or muscle cramps
• Mood changes, like depression or feelings of sadness
• Not sleeping well
• Hair loss
• Loss of appetite
• Getting sick more easily
• Pale skin

If you’re exhausted, your bones hurt, you have muscle weakness or mood changes, that’s an indication that something may be abnormal with your body^[5]. However, you may have no signs or symptoms of vitamin D deficiency at all^[1].

Causes of Vitamin D Deficiency

You can become deficient in vitamin D for different reasons^[2]:

• You don’t get enough vitamin D in your diet
• You don’t absorb enough vitamin D from food (a malabsorption problem, where the digestive system cannot properly take in nutrients)
• You don’t get enough exposure to sunlight
• Your liver or kidneys cannot convert vitamin D to its active form in the body
• You take medicines that interfere with your body’s ability to convert or absorb vitamin D

The primary source of vitamin D is via ultraviolet radiation from sunlight on the skin. When ultraviolet rays strike the skin, the skin synthesizes vitamin D. However, the body makes most vitamin D when the skin is exposed to sunlight, and between October and early March in some regions, people do not make enough vitamin D from sunlight^[7].

People can also get vitamin D from certain foods and dietary supplements, but it is difficult to obtain enough vitamin D from diet alone^[2].

Who is at Higher Risk?

Some people are at higher risk of vitamin D deficiency^[2]:

• Breastfed infants, because human milk is a poor source of vitamin D. If you are breastfeeding, your infant should receive a supplement of 400 IU of vitamin D every day
• Older adults, because their skin doesn’t make vitamin D when exposed to sunlight as efficiently as when they were young, and their kidneys are less able to convert vitamin D to its active form
• People with dark skin, which has less ability to produce vitamin D from the sun. People with darker skin are much better protected from UV rays but also need to spend more time in the sun than people with lighter skin to produce the same amount of vitamin D^[5]
• People with conditions that make it difficult to absorb nutrients from food, such as Crohn’s disease, ulcerative colitis, and celiac disease
• People who have obesity, because their body fat binds to some vitamin D and prevents it from getting into the blood
• People who have had gastric bypass surgery, which creates a bypass of part of the small intestine where vitamin D is absorbed
• People with chronic kidney or liver disease, which can affect the ability to change vitamin D into a form the body can use
• People who take medicines that affect vitamin D levels, including certain cholesterol, anti-seizure, steroid, and weight-loss medicines

People who are not often outdoors, are in an institution like a care home, or usually wear clothes that cover up most of their skin when outdoors are also at risk^[7]. Your geographical location may also prevent adequate vitamin D exposure through sunlight^[1].

How is it Diagnosed?

Measurement of serum 25-hydroxyvitamin D (25[OH]D) is the best test to determine vitamin D status^[3]. This blood test measures how much vitamin D is in your body^[2].

Levels of 25(OH)D are interpreted as follows^[3]:

• Below 20 ng/mL (50 nmol/L): Vitamin D deficiency
• 20 to 30 ng/mL (50 to 75 nmol/L): Vitamin D insufficiency
• Above 30 ng/mL: Adequate vitamin D levels

Although not always required for diagnosis, measurement of the serum parathyroid hormone (PTH) level may help establish the diagnosis of insufficiency. PTH levels are often elevated in patients with vitamin D insufficiency, indicating secondary hyperparathyroidism^[11].

Screening for vitamin D deficiency is recommended only in individuals who are at high risk for vitamin D deficiency^[12]. The Endocrine Society recommends against screening for vitamin D deficiency in most healthy adults^[3].

Getting Enough Vitamin D

You can get vitamin D in three ways: through your skin from sunlight, from your diet, and from supplements^[2].

Sunlight

Your body forms vitamin D naturally after exposure to sunlight. When sunlight hits the skin, the skin converts that ultraviolet radiation to vitamin D^[4]. From about late March or early April to the end of September, most people should be able to make all the vitamin D they need from sunlight^[7].

The body can only absorb a limited amount of vitamin D at a time. Spending extra time in the sun won’t increase vitamin D levels but will increase your risk of skin cancer^[1]. Too much sun exposure can lead to skin aging and skin cancer, so many people try to get their vitamin D from other sources^[2].

Sun protection is recommended whenever UV levels reach 3 and above^[23]. During these times, use sunscreen, hats, clothing, sunglasses, and shade, but also make time to get some sun exposure for vitamin D production.

Food Sources

There are few foods that naturally have some vitamin D^[2]:

• Fatty fish such as salmon, tuna, mackerel, trout, and herring
• Canned fish like sardines
• Beef liver
• Cheese
• Mushrooms
• Egg yolks
• Fish liver and cod liver oil

Since there aren’t a lot of naturally occurring vitamin D foods, many products are enriched with vitamin D. Foods that often have added vitamin D include^[2]:

• Milk
• Breakfast cereals
• Orange juice
• Other dairy products, such as yogurt
• Soy drinks
• Almond milk
• Some spreads and margarine

Always check the nutrition label to ensure there’s vitamin D added^[5].

Recommended Amounts

The amount of vitamin D you need each day depends on your age. The recommended amounts, in international units (IU), are^[2]:

• Birth to 12 months: 400 IU
• Children 1-13 years: 600 IU
• Teens 14-18 years: 600 IU
• Adults 19-70 years: 600 IU
• Adults 71 years and older: 800 IU
• Pregnant and breastfeeding women: 600 IU

Treatment

If you have vitamin D deficiency, the treatment is with vitamin D supplements^[2]. Vitamin D is in many multivitamins, and there are also vitamin D supplements available in pills and in liquid form for babies^[2].

Vitamin D has two main forms: D2 (ergocalciferol) and D3 (cholecalciferol). You can absorb both types in your body, but studies have shown that vitamin D3 raises your levels more effectively than vitamin D2^[5].

Recommended treatment for vitamin D-deficient patients varies by age^[12]:

Up to age 1 year:

• 2000 IU/day of vitamin D2 or D3 for 6 weeks, or 50,000 IU of vitamin D2 or D3 once weekly for 6 weeks
• When the serum 25(OH)D level exceeds 30 ng/mL, provide maintenance treatment of 400-1000 IU/day

Ages 1-18 years:

• 2000 IU/day of vitamin D2 or D3 for at least 6 weeks, or 50,000 IU of vitamin D2 once weekly for at least 6 weeks
• When the serum 25(OH)D level exceeds 30 ng/mL, provide maintenance treatment of 600-1000 IU/day

Adults:

• 50,000 IU of vitamin D2 or D3 once weekly for 8 weeks, or 6000 IU/day of vitamin D2 or D3 for 8 weeks
• When the serum 25(OH)D level exceeds 30 ng/mL, provide maintenance treatment of 1500-2000 IU/day

A doctor may prescribe a prescription-strength dose of vitamin D if your levels are severely low^[5]. Most adults should be taking a vitamin D supplement, with over-the-counter supplements containing vitamin D3 recommended. The recommended dosage of vitamin D for most adults is 1000-2000 international units daily^[1].

Vitamin D supplements are generally safe. A vitamin D supplement doesn’t cause many adverse effects at recommended doses. What you don’t use, your body usually urinates out, so it’s difficult to overdose on vitamin D unless you are taking massive doses^[5]. However, extremely high levels of vitamin D are harmful and can cause nausea, vomiting, confusion, excessive thirst, and kidney stones^[5].

Vitamin D supplements can interact with certain medications, so check with your doctor before starting one^[5]. Treatment may also include dietary modifications and adequate sun exposure, along with supplementation^[3].

Outlook

Vitamin D deficiency is preventable and treatable^[1]. Adding an over-the-counter vitamin D supplement can make improvements in just three to four months^[20].

The goal of treatment is to normalize vitamin D levels to relieve symptoms and decrease the risk of fractures, falls, and other adverse health outcomes^[11]. With proper supplementation and attention to sun exposure and diet, vitamin D levels can be restored to normal ranges.

Therapy and prevention of vitamin D deficiency are straightforward, relatively inexpensive, and safe^[4]. If you have questions about your vitamin D intake or suspect you may have a deficiency, consult with your healthcare provider. They can do a blood test to check your vitamin D levels and recommend appropriate treatment if needed.