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Soak in the sun: Vitamin D for bone health

1 Apr 2021

For long, it is known that vitamin D and calcium are a necessity for healthy bones. Recent studies have uncovered that it may have a much wider role in the body’s metabolic processes. “Vitamin D plays an important role in bone formation, and therefore, individuals with low bone density or fragility fractures need to be tested for deficiency,” says Dr Biswajit Dutta Baruah, consultant orthopaedic surgeon, KIMS Oman hospital.

Lira had been coming into the clinic for some time. A very active person otherwise, but due to the corona pandemic, she had been restricting her activities to within the house. The reason she was coming in to see me was because of the aches and pains that were bothering her. I ran X-rays for her spine and checked her blood. Everything came out negative. 

“Doctor, I’ve never felt this tired before. So out of energy, when I return home, I feel like collapsing into the bed,” she blurted out in exhaustion. “May be, you caught the virus,” I offered an explanation defensively. 

I sent her over to the physician knowing that viral infections are known to cause extreme fatigue. He ran tests to detect the viral antibody. It was a great relief for both patient and doctor to know that it was negative. Finally, I made up my mind to check her vitamin D levels, given that she was indoors most of the time glued to the laptop screen attending virtual meetings.

Vitamin D is unique among all the vitamins. It is a naturally occurring fat soluble steroid that qualifies as a micronutrient as its deficiency can be treated by supplementation. It is also a pro-hormone as it needs to be activated in the body to be functional. For long, it is known that vitamin D and calcium are a necessity for healthy bones. Recent studies have uncovered that it may have a much wider role in the body’s metabolic processes. It was the fourth vitamin to be identified in cod liver oil by Elmer McCollum (an American researcher), thus deriving its name from the fourth letter of the English alphabet.


Dietary sources of vitamin D

Dietary sources of vitamin D are limited to oily fish, milk or milk products like yoghurts, labaan, cheese and paneer that are fortified with vitamin D. Fortification is the process of adding extra nutrients to food at the time of processing, for example vitamin D is added to milk at the milk factory or iodine is added to salt. Many cereal manufacturers also fortify their products with minerals and vitamins (including vitamin D). However such food items may not be consumed uniformly by all or may be considered expensive for daily consumption. Thereby, for most people dietary sources of vitamin D are very limited or even nil. Majority of the people obtain vitamin D from skin exposure to Ultraviolet B (UVB) radiation in sunlight. Alfred Fabian Hess, an American physician, once famously said, “Light equals vitamin D”. UVB in sunlight is maximum from 10 am to 3 pm, however exposing oneself to the harsh sunlight during this period is not practical. The amount of UVB that reaches the skin is also limited by the type or amount of clothing that covers the skin, use of sunscreens, greater age and darker pigmentation of the skin. This explains why vitamin D deficiency can be profound even in sunny regions like Muscat. In normal times, elderly people who are homebound commonly develop vitamin D deficiency due to limited sun exposure.


Activation of vitamin D

There are two biological forms of vitamin D, ergocalciferol (D2) and cholecalciferol (D3). vitamin D3 is the vitamin that is produced by skin exposure to sunlight. Mushrooms have been used in the past for commercially producing large quantities of plant source of vitamin D2. Just as in case of vitamin D3, the mushrooms need to be exposed to sunlight to produce vitamin D2. Mushrooms available in the grocery  stores, thereby have very small quantities of vitamin D2.

Whether obtained from the mushrooms or by sunlight, exposure the vitamin D obtained is still not functional in the body. It needs to be activated by a process called hydroxylation in two steps, first in the liver and then in the kidney, resulting in the active form of the vitamin. Due to this reason, vitamin D is technically not a vitamin (because it is inactive) and referred to by some as a prohormone. It follows naturally that an individual needs functional kidneys and a liver for the vitamin D to be useful. It is expected that those with chronic kidney or liver disease are likely to develop vitamin D deficiency.

Studies have found 25% to 50% of patients in clinical practice to be deficient in vitamin D. Despite this being a large number, vitamin D testing is expensive and, at present, not universally recommended. Patients at high risk would be those with gut disorders resulting in decreased absorption, diseases affecting the kidney or the liver and those in whom Sun exposure is limited. 

Vitamin D plays an important role in bone formation, and therefore, individuals with low bone density or fragility fractures (fractures that occurred with low intensity forces that would not result in a fracture in a normal person) need to be tested for deficiency.

Several studies have suggested that symptoms like bone pain, myalgias and generalised weakness or fatigue are often associated with vitamin D deficiency. These are often misdiagnosed as fibromyalgia, chronic fatigue or age-related weakness. However a cause-effect relationship between the two is yet to be established, and routine testing in such situations is not yet the norm.

Vitamin D deficiency can also be a surrogate marker (indicator) for poor nutritional status and lack of outdoor activity, especially in children.

Ingested or skin produced vitamin D is quickly activated in the liver and kidney, to an intermediate form (25-hydroxy vitamin D or calcifediol) and a final activated form (1,25-dihydroxy vitamin D or calcitriol). However, a small amount of the activated form exists in the blood. Hence, almost all lab studies detect the intermediate form of vitamin D. Doctors order this test to make a diagnosis. Though vitamin D is necessary to mobilise calcium into the bones and its absorption in the intestines, most people assume that calcium will be deficient in blood. However, low vitamin D levels result in increased secretion of parathormone – a hormone release by the parathyroid glands, resulting in release of calcium from bone and increased absorption of calcium by the kidney. This causes blood levels of calcium to remain normal in spite of deficiency. Similarly it is erroneous to measure the levels of calcitriol in blood as these levels are low in normal individuals and is not an indicator of true deficiency.


Immunity indicator

Deficiency of vitamin D can cause rickets in children and osteomalacia in adults. In both the conditions, bone is soft and often associated with deformities or non-trauma related fractures. Rickets is well controlled these days due to its easy recognition among pediatricians and easy supplementation. Vitamin D supplementation is inexpensive and safe. Many patients worry if taking high doses of vitamin D can be toxic. This is not possible due to safety mechanisms in the body. High levels of calcitriol (activated vitamin D) will inhibit the activation process in the kidney thus limiting its availability. So vitamin D toxicity is very rare. Though marketed by many for its anti-cancer properties, studies have not found strong evidence to support this claim. A few studies have found lower mortality rates (death rates) but do not show meaningful reduction of the occurrence of stroke, heart attacks or chest pain. 

Several studies have claimed that vitamin D activates the immune system, and its deficiency has been linked to increased risk of developing viral infections including COVID. 

As discussed earlier, this may simply be an indicator of poor nutritional status. Whether vitamin D supplementation will mitigate (decrease) this risk is not yet known. 

Once diagnosed to be deficient, the doctor will start large weekly doses in the range of 50000 to 60000 IU/week. This is called loading dose. After 8-12 weeks of this high dose therapy, the doses are tapered (decreased) to about 1000-2000IU/day for another 8-12 weeks. It goes without saying that sufficient exposure to sunlight by walking early morning or late afternoon can also help in bringing vitamin D levels back to normal. 


Sit in the Sun

Lira was diagnosed with vitamin D deficiency. Calcifediol levels were very low in her blood sample. She was started on vitamin D supplements. She was also asked to walk outside daily and sit next to the window with drapes open. She will need to come back in 6 months to check if her vitamin D levels in blood have been restored to normal. 

To summarise, vitamin D is important for both bone and non-skeletal health. It is well established that vitamin D deficiency is rampant in society. Vitamin D is mostly produced in the body by exposure to sunlight. Testing for the intermediate form will reveal if a person is deficient. Supplements are necessary and sufficient to restore levels back to normal.




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