Role of Vitamin D & Vitamin D Deficiency
Role of Vitamin D
Vitamin D through its active form (1,25-dihydroxyvitamin D) is essential for intestinal Ca absorption and plays a central role in maintaining Ca homeostasis and skeletal integrity1
In vitamin D deficiency there is a decrease in the concentration of 25(OH) vitamin D (25-hydroxy vitamin D) and an increase of varying degrees in the parathyroid hormone (PTH) level2
The increased serum PTH stimulates bone turnover, leading to bone loss3
In periods of protracted vitamin D deficiency, bone loss is increased and this may lead to osteoporosis3
Definition of vitamin D deficiency
“There is widespread acknowledgement of the presence of vitamin D deficiency in the community and the pressing need to address this deficiency1“
Prof Kevin Cashman, UCC, commenting on the results of the Irish NANS Study 2013.
- The North American Institute of Medicine (IOM)’s DRI Committee for Ca and vitamin D proposes a serum 25(OH)D concentration of 50nmol/Lthat would meet the needs of 97.5% of normal healthy persons1
In agreement with the Scientific Advisory Committee on Nutrition (SACN) and Institute of Medicine (IOM) reports, the National Osteoporosis Society (NOS)4 in the UK proposes vitamin D thresholds as follows:
Plasma 25 (OH) D < 25 nmol/L is deficient
Plasma 25 (OH) D of 25 – 50 nmol/L may be inadequate in some people
Plasma 25 (OH) D > 50 nmol/L is sufficient for almost the whole population
- The Endocrine Society Clinical Practice Guideline defines vitamin D deficiency as 25(OH)D below 50nmol/L and vitamin D insufficiency below the range of 52.5-72.5nmol/L5
- The American Geriatrics Society Consensus Statement on Vitamin D for the Prevention of Falls and their Consequences recommends that a serum 25(OH)D concentration of 75nmol/L should be a minimum goal to achieve in older adults, particularly in frail adults who are at greater risk of falls, injuries and fractures6
- The guideline statement from the Scientific Advisory Council of Osteoporosis Canada states that the optimal level of serum 25(OH)D for musculoskeletal benefits is >75nmol/L7
- The American Academy of Paediatrics (AAP) states that serum concentrations of 25(OH)D in infants and children should be at least 50nmol/L8
- The Canadian Paediatric Society defines deficiency as serum 25(OH)D levels <25 nmol/l, insufficiency as 25-75nmol/L but highlights a range of 75-225nmol/L as optimal for parathyroid hormone production, minimisation of resorption from bone and stabilisation of intestinal calcium absorption9
- The Evidence-Based Recommendations from the Cystic Fibrosis Foundation, published in JCEM 2012, recommend a minimum serum 25(OH)D level of 75nmol/L for people with cystic fibrosis10
Clinical features of vitamin D deficiency
- In young children, who have little mineral in their skeleton, vitamin D deficiency results in a variety of skeletal deformities classically known as rickets5
- In adults, the epiphyseal plates are closed and there is enough mineral in the skeleton to prevent skeletal deformities so that this mineralisation defect, known as osteomalacia, often goes undetected5
- However osteomalacia causes a decrease in Bone Mineral Density (BMD) and is associated with isolated or generalised aches and pains in bones and muscles5
Impact of bone structure on osteomalacia11
Osteomalacia is softening or weakening of the bones due to a lack of vitamin D or due to a problem with the body’s ability to break down and absorb vitamin D.
- Vitamin D deficiency causes muscle weakness
- Affected children have difficulty standing and walking
- The elderly have increasing sway and more frequent falls, thereby increasing their risk of fracture5
The pathophysiologic pathways from vitamin D deficiency to osteoporosis, osteomalacia, falls and fractures:3
1. Cashman K et al. Vitamin D status of Irish adults: findings from the National Adult Nutrition Survey. British Journal of Nutrition (2013), 109, 1248-1256.
2. Haroon M and Regan M. Vitamin D deficiency: the time to ignore it has passed. International Journal of Rheumatic Diseases 2010; 13: 318-323.
3. Lips et al. The effect of vitamin D on bone and osteoporosis. Best Practice & Research Clinical Endocrinology & Metabolism 25, (2011), 585-591.
4. National Osteoporosis Society (NOS). Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management. December 2018. V2.
5. Holick M et al. Evaluation, Treatment, and Prevention of Vitamin D Deficiency: an Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab; July 2011; 96(7): 1911-30.
6. Recommendations Abstracted from the American Geriatrics Society Consensus Statement on Vitamin D for Prevention of Falls and Their Consequences. J Am Geriatr Soc 62: 147-152, 2014.
7. Hanley D et al. Vitamin D in adult health and disease: a review and guideline statement from Osteoporosis Canada (summary). CMAJ 2010, Sep 7; 182(12): 1315-1319.
8. Wagner C et al. Prevention of Rickets and Vitamin D Deficiency in Infants, Children, and Adolescents. Paediatrics Vol 122: No. 5 November 1, 2008, 1142-1152.
9. Godel J et al. Recommendations for Canadian mothers and infants. Paediatr Child Health 2007; 12(7): 583-9.
10. Tangpricha V et al. An Update on the Screening, Diagnosis, Management and Treatment of Vitamin D Deficiency in Individuals with Cystic Fibrosis: Evidence-Based Recommendations from the Cystic Fibrosis Foundation. J Clin Endocrinol Metab April 2012, 97(4): 1082-1093.
11. http://blogs.longwood.edu/osteomalacia/2012/07/06/what-is-osteomalacia/ accessed 24/10/17