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Vitamin D insufficiency has several negative consequences for spinal cord injured individuals. Vieri Failli, biologist, gives some insights into the topic.

Vitamin D insufficiency is common in spinal cord injured individuals. This is due to the presence of many contributing factors including limited sun exposure and intake, use of medication and endocrine perturbations. Although there are several biological plausible mechanisms by which vitamin D may act upon musculoskeletal and cardio-metabolic health, the impact of vitamin D insufficiency on such systems remains unclear in spinal cord injured individuals.

All about Vitamin D
Vitamin D is the generic name of a vitamin which has several distinct forms, called vitamers. Vitamin D is classified into five different classes numbered from 1 to 5. In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol). Vitamin D, a fat-soluble vitamin, is only contained in a few foods like fish and egg yolk. The major natural source of the vitamin is synthesis of cholecalciferol in the skin from cholesterol through a chemical reaction that is dependent on sun exposure. When the body receives Vitamin D (from sunlight, food, or supplements), it turns the Vitamin D into an activated Vitamin D called calcitriol.

Effects of vitamin D insufficiency
One of the most important roles of vitamin D is to maintain skeletal calcium balance. Deficiency, or hypovitaminosis D, most commonly results from inadequate sunlight exposure. Deficiency impairs bone mineralization, leading to bone softening diseases such as osteoporosis and increase the risk of bone fractures. Muscle weakness is also a common symptom of vitamin D deficiency, further increasing the risk of fall and fracture in adults. Other problems include depression, light-headedness and periodontitis.

Vitamin D deficiency after spinal cord injury
Numerous studies reported that individuals with an acute or chronic spinal cord injury have a vitamin D deficiency. Overall, the prevalence of this deficiency seems to be high (range: 32-93%) in this population compared with that in able-bodied persons. The main factors are immobility, low physical activity and bedrest, and therefore not enough exposure to sunlight. Other factors that can influence the degree of deficiency include age, skin pigmentation, lesion level, occurrence of pressure ulcers, body mass index, season and latitude. Just as in the general population, vitamin D deficiency for spinal cord injured individuals can create several problems, of which the most common is bone deterioration. However, in this population hypovitaminosis D seems to have further implications.

Vitamin D as a predictor of worsening physical function
A recent study conducted in Italy found that low vitamin D levels in people with chronic spinal cord injury could predict a worsening in physical function one year later. The study was based on sixty-seven patients (44 men and 23 women) with chronic SCI admitted to a rehabilitation program. After measuring their serum vitamin D levels, clinicians assessed their physical function. These tests included functional independence in daily living activities (SCIM III) and leisure time physical activity (LTPA) which were then repeated exactly one year later.

Analysis revealed that a low level of vitamin D in the serum could successfully predict a worsening in physical function.

However, further work is needed to understand how the hypovitaminosis D is linked to this worsening, and eventually if it could be decreased in any way.

As this measure offers a powerful tool to evaluate which chronic patients might be at risks for future complications, routine screening and monitoring of vitamin D as well as treatment of deficiencies should be established in both acute and chronic setting. 

Vitamin D and functional recovery
We already know from studies that Vitamin D has a strong modulatory effect on the immune system, controlling the activity several types of immune cells. Another interesting aspect is the fact that both neurons and glia express receptors of vitamin D on their membranes. In both cell types, vitamin D seems in fact to control the intracellular calcium levels. This observation led several research group to test the efficacy of a vitamin D treatment in experimental spinal cord injury models. Independent groups found that a vitamin D treatment seems to improve functional recovery. Moreover, this recovery was paralleled by an anatomical salvage, suggesting that the functions that were recovered relied on a higher number of fibers innervating the distal part of the injury. However, this effect was reported only when the treatment was delivered as early as possible (ideally 24 hours after the injury) and not later than a week after the injury, still making it a rather exploitable window of opportunity.

Most adults are believed to be at least somewhat deficient in vitamin D, however, people with a spinal cord injury have an even greater chance to be deficient and should be particularly aware of it consequences. If longer sun exposure is not possible, people should also consider incorporating food rich in this vitamin within their regime.

Yours Vieri Failli

Vieri Failli is a doctor of neuroscience, but has a passion for bringing the general public closer to the most complex questions of science.
Vieri Failli is a doctor of neuroscience, but has a passion for bringing the general public closer to the most complex questions of science.