Vitamin D: Definition, deficiency, supplement & toxicity

Vitamin D is a group of fat-soluble secosteriods, that is required for the regulation of minerals, calcium and phosphorus in the body. It also helps in maintaining proper bone structure through out life.

Exposure of the hands, face, arms, and legs to sunlight for at least 2-3 times a weeks is an easy, reliable way for most people. Although the necessary exposure time varies with age, skin type, season, time of day, and many more factors. It’s storage takes place in our body’s fat during sunlight and then released after sunlight is gone.  




Good sources of vitamin D 

There are a number of good food sources you can relay on for adequate forms. Vitamin D is mostly needed to keep our bones, teeth and muscles healthy.

Conditions like rickets (bone deformity) in children, and osteomalacia characterized by chronic bone pain in adults, are as a result of lack of this nutrient.

Good sources include 

  • Salmon
  • Sardines
  • Herring 
  • Mackerel
  • Red meat
  • Liver
  • Eggs
  • Cereals





Sunlight  is a well known source, and less sunlight typically means less vitamin D.

However, people living in sunny climates who always stay indoor, wear that covers their entire body when outside, or use sunscreens to reduce skin cancer risk are also at risk of deficiency.

While in Africa the deficiency is mainly linked with malnutrition and poverty.

Older people are also at risk for VDD. They are less likely to spend time in the sun, have fewer “receptors” in their skin that convert sunlight to the active form, may not get enough in their diet, may have trouble absorbing it even if they do get it in their diet, and may have more trouble converting It to a useful form due to kidney problems.

Scientists suggest that the risk for VDD in people over 65 years of age is very high. 





While it is quite difficult for people to get enough from food alone, older people, those living in northern latitudes, dark skinned individuals, pregnant and breastfeeding women should consider taking a daily supplement as required.

The World Health Organisation says; Infants are born with low stores and are dependent on breast milk, sunlight or supplements as sources in the first few months of life.

As the vitamin D content of breast milk is dependent on maternal vitamin D status and this is often low, sun exposure may be restricted for infants living at higher latitudes or for cultural or other reasons, infants are particularly vulnerable deficiency.

Deficiency in infants can lead to bone malformation (rickets), seizures and difficulty breathing. 

It is important as an adult to seek advice from your health care provider whether or not supplementation is best for you.





Vitamin D toxicity is rare. It is caused by supplementing with high doses rather than sunlight resulting in hypercalcemia. 

Hypercalcemia is associated with  increase in urination and thirst. If left untreated, hypercalcemia may result in excess deposits of calcium in soft tissues and organs such as the kidneys, liver, and heart, resulting in pain and organ damage.


Symptoms hypercalcemia including;

  • Anorexia
  • Nausea
  • Vomiting
  • Excessive urination 
  • Intense thirst
  • Body weakness
  • Difficulty sleeping 
  • Nervousness
  • Itching 
  • Renal failure
  • Mental retardation


In young children,

  • Abnormal bone growth and formation
  • Diarrhea
  • Irritability
  • Weight loss
  • Severe depression


Vitamin D toxicity is treated by discontinuing supplementation and restricting calcium intake. Kidney damage may be irreversible. 

People with as kidney disease, lymphoma, sarcoidosis, arteriosclerosis, hyperparathyroidism, tuberculosis and histoplasmosis have increased sensitivity and  are more likely to develop hypercalcemia in response to any increase.

Maternal hypercalcemia increases fetal sensitivity to effects of vitamin D during pregnancy causing mental retardation and facial deformities. It is advisable to use vitamin D cautiously.











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