The role of vitamin D and the treatment of vitamin D deficiency

Vitamin D

Vitamin D through its active form (1,25-dihydroxyvitamin D) is essential for intestinal calcium absorption and plays a central role in maintaining calcium homeostasis and skeletal integrity.¹

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) level.²

The increased serum PTH stimulates bone turnover, leading to bone loss.³

In periods of protracted vitamin D deficiency, bone loss is increased, and this may lead to osteoporosis.³

Vitamin D deficiency

“There is widespread acknowledgement of the presence of vitamin D deficiency in the community and the pressing need to address this deficiency.”¹
— 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 calcium and vitamin D proposes a serum 25(OH)D concentration of 50 nmol/L that would meet the needs of 97.5% of normal healthy persons.¹

In agreement with the Scientific Advisory Committee on Nutrition (SACN)² report, the Royal Osteoporosis Society (ROS)³ in the UK proposes vitamin D thresholds as follows:

Plasma 25(OH)D < 25 nmol/L is deficient
Plasma 25(OH)D 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 50 nmol/L and vitamin D insufficiency below the range of 52.5–72.5 nmol/L.⁴

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 75 nmol/L should be a minimum goal to achieve in older adults, particularly in frail adults who are at greater risk of falls, injuries, and fractures.⁵

The guideline statement from the Scientific Advisory Council of Osteoporosis Canada states that the optimal serum 25-hydroxyvitamin D (25OHD) level for bone health is uncertain; however, ≥50 nmol/L is generally considered adequate for bone and overall health in healthy individuals.⁶

The American Academy of Pediatrics (AAP) states that serum concentrations of 25(OH)D in infants and children should be at least 50 nmol/L.⁷

The Canadian Paediatric Society defines deficiency as serum 25(OH)D levels <25 nmol/L, insufficiency as 25–75 nmol/L, but highlights a range of 75–225 nmol/L as optimal for parathyroid hormone production, minimisation of bone resorption, and stabilisation of intestinal calcium absorption.⁸

The Evidence-Based Recommendations from the Cystic Fibrosis Foundation, published in JCEM (2012), recommend a minimum serum 25(OH)D level of 75 nmol/L for people with cystic fibrosis.⁹

Clinical Features of Vitamin D Deficiency

Osteomalacia and vitamin D deficiency treatment

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

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

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.
Scientific Advisory Committee on Nutrition (SACN) Vitamin D and Health Report, 2016, P 1 – 285
The Royal Osteoporosis Society (ROS). Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management.December 2018. V2.
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.
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.
Morin et al, Appendix 1 2023 Guideline Supplementary Tables in Clinical practice guideline for management ofosteoporosis and fracture prevention in Canada: 2023 update, CMAJ October 10, 2023 195 (39) E1333-E1348.
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.
Godel J et al. Recommendations for Canadian mothers and infants. Paediatr Child Health 2007; 12(7): 583-9, Reaffirmed January 2017.
Tangpricha V et al. An Update on the Screening, Diagnosis, Management and Treatment of Vitamin D Deficiency inIndividuals with Cystic Fibrosis: Evidence-Based Recommendations from the Cystic Fibrosis Foundation. J Clin EndocrinolMetab April 2012, 97(4): 1082-1093.

IE-ALT-385(2) November 2025