Vitamin D deficiency (VDD) has emerged as a global problem over the last decade. Undiagnosed vitamin D deficiency is also quite common.

What Is Vitamin D

Vit D is a fat-soluble vitamin which is sometimes called the sunshine vitamin because our body makes it from cholesterol when our skin is exposed to sunlight.

Role In The Body

Vitamin D plays a crucial role in maintaining the balance of calcium in your blood and bones and building and maintaining bones. 

Specifically, your body needs vit D to utilize calcium and phosphorus for bone-building and tissue support. 

Chronic and/or severe vitamin D deficiency causes a decline in calcium and phosphorus absorption by your intestines, resulting in hypocalcemia (low calcium levels in your blood) and secondary hyperparathyroidism (overactive parathyroid glands attempting to regulate blood calcium levels).

Symptoms such as muscle weakness, cramps, fatigue, and depression may occur due to both hypocalcemia and hyperparathyroidism if they are severe. 

To address low calcium levels in your blood through secondary hyperparathyroidism, your body withdraws calcium from your bones, leading to accelerated bone demineralization (the breakdown of bones surpasses their formation). This process can result in osteomalacia (soft bones) in adults and rickets in children.

It may even help prevent cancer and protect against several chronic conditions, including

• Depression
• Type 2 diabetes
• Heart disease

Sources

Humans get vit D from exposure to sunlight, from their diet, and dietary supplements.

• The major source of Vit D is formation in the skin with the help of ultraviolet-B rays (UV-B) of sunlight.
• In India, a daily sunlight exposure of 17-30 min in infants and 30-45 min in older children over 15-40% body surface area is recommended at least five times a week during noon (11 AM-3 PM) for preventing vit D deficiency.

Note: Because any excess Vit D is destroyed by sunlight, excessive exposure to sunlight does not cause vitamin D toxicity

• Among the dietary sources, vit D is mainly obtained from animal sources like fish, liver, cod liver oil, and eggs.
• It is also found in plants, especially mushroom
• Vitamin D-fortified foods are also a source.

What is Vitamin D Deficiency

Vit D deficiency occurs when we don’t have enough of it in our body.

Although there is no consensus on optimal vit D levels in blood, deficiency is generally diagnosed at blood levels of <12 ng/mL. A level of  >20 ng/mL is considered sufficient. ≥12-20 ng/mL of Vitamin D is insufficient. 

Causes Of Vitamin D Deficiency

Causes of deficiency are:

Reduced formation in the skin

This occurs due to sunscreen use, covered clothing, skin pigmentation, skin grafts, and aging.

Note: Darker skin may not get enough vit D through sunlight.

Poor absorption

This can occur in disorders of absorption of dietary Vit D (Malabsorption), bypass surgery, and obesity.

Kidney diseases

The kidney is involved in the activation of Vit D. Patients with kidney disease also have vit D deficiency.

Liver diseases

The Liver is involved in Vitamin D formation, and liver failure leads to deficiency.

Genetic Disorders

Certain genetic diseases of Vit D metabolism lead to its deficiency. 

Vitamin D Deficiency Symptoms in Adults

Osteomalacia happens when bones in adults don’t get enough minerals to stay strong as they naturally replace old bone tissue with new. This leads to a gradual loss of minerals from the bones, even though the bone structure itself is okay. 

The result? Painful bones, misshapen skeletons, and weaker muscles.

Women who don’t get enough vit D, especially after having several pregnancies, are more likely to develop osteomalacia. This is because their bodies have to use up a lot of calcium to help their babies grow strong bones before birth and to produce milk for breastfeeding.

Elderly people are also at risk of osteomalacia. As people age, their skin makes less of a substance called 7-dehydrocholesterol, which the body uses to produce vitamin D when exposed to sunlight. Plus, many older adults don’t spend as much time in the sun, which means they may not get enough vitamin D to keep their bones healthy.

Vitamin D Deficiency Symptoms in Children

Rickets is a condition that affects young children and adolescents when their bones don’t get enough minerals to become strong. In babies, this means that the soft cartilage at the ends of bones keeps growing but doesn’t harden into proper bone. One early sign of rickets is a soft spot on the baby’s head that takes longer to close up than usual.

As rickets progresses, the ends of bones can swell up, especially where the ribs meet the cartilage. This can make the ribcage look like it has beads on it, which is called a “rachitic rosary.” In severe cases, this can even cause the chest to cave in, making it hard to breathe.

When a child with rickets starts to walk, their weight can bend their soft bones, leading to bowed legs or knees that knock together. This can also affect the shape of the pelvis. Similar bone problems can happen during the teenage growth spurt.

In very severe cases, not having enough calcium in the blood can cause muscle spasms called tetany because the body can’t maintain the right balance of minerals inside cells.

Requirements And Treatment

Adequate daily intake of vitamin D is:

• 200 IU (International units) for children and adults up to 50 years of age
• 400 IU for adults 51 to 70 years of age
• 600 IU for adults 71 years of age or older

Treatment of Vit D Deficiency is by oral or injectable Vit D supplementation along with oral calcium supplementation. The duration and dosage depend on the clinical condition and the severity of the deficiency.

Vitamin D Toxicity

A blood level of  >100 ng/mL defines vit D toxicity which might occur due to excessive supplementation. This may cause increased blood levels of calcium in blood and urine.

Summary

Vitamin D deficiency occurs surprisingly commonly, but its symptoms are often subtle and nonspecific, making it difficult to determine whether one has a deficiency or another health condition. If you suspect a deficiency, consult a healthcare professional for a blood test. Treatment for deficiency typically involves supplements and dietary and lifestyle adjustments.

References

1. Bender, D. A. (2010). Nutritional biochemistry of the vitamins. Cambridge University Press. 
2. Chang, S.-W., & Lee, H.-C. (2019). Vitamin D and health – the missing vitamin in humans. Pediatrics &amp; Neonatology, 60(3), 237–244. https://doi.org/10.1016/j.pedneo.2019.04.007 
3. Gupta P;Dabas A;Seth A;Bhatia VL;Khadgawat R;Kumar P;Balasubramanian S;Khadilkar V;Mallikarjuna HB;Godbole T;Krishnamurthy S;Goyal JP;Bhakhri BK;Ahmad A;Angadi K;Basavaraj GV;Parekh BJ;Kurpad A;Marwaha RK;Shah D;Munns C;Sachdev HPS; (n.d.). Indian Academy of Pediatrics Revised (2021) guidelines on prevention and treatment of vitamin D deficiency and rickets. Indian pediatrics. https://pubmed.ncbi.nlm.nih.gov/34969941/ 
4. Holick, M. F. (2007). Vitamin D deficiency. New England Journal of Medicine, 357(3), 266–281. https://doi.org/10.1056/nejmra070553 
5. Sizar, O. (2023, July 17). Vitamin D deficiency. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK532266/