There is a well-established high prevalence of osteoporosis and fractures in the learning disabilities population. The estimated cost of a hip fracture in the UK is £12,000 for hospital costs and £13,000 in the first 2 years for health and social after care, so measures are needed to reduce fractures in this population.

Roughly thirty-percent of people with learning disabilities take anti-epileptic drugs (AEDs), a long known cause and risk factor for low bone-mass density and fractures. Why this is, researchers don’t definitively know, but it may have to do with AEDs negatively affecting vitamin D catabolism (breaking down vitamin D stores in the body at a higher rate than normal) (Meier C et al, 2011). This means that AEDs can cause vitamin D deficiency, which in turn may lead to osteoporosis and osteomalaica (Ooms ME et al, 2011; Macdonald HM et al, 2013) and increase risk of fracture (since vitamin D is intimately involved in calcium absorption and bone health) (Bischoff-ferrari HA et al, 2012).

To date, there hasn’t been much research on vitamin D deficiency in the learning disabilities population and whether it’s exclusive to those on AEDs. Might vitamin D deficiency explain the increased risk of osteoporosis and fractures in people with learning disabilities? Are people with learning disabilities more likely to have vitamin D deficiency or only those taking AEDs?

In a new study published in The British Journal of Psychiatry (Frighi et al, 2014), researchers from the University of Oxford took steps to better answer these questions, particularly the question of whether people with learning disabilities are more likely to have vitamin D deficiency.

Methods

In a case-control study, researchers measured the vitamin D levels [25(OH)D] in 155 people with learning disabilities. These people were enrolled in the Oxford Learning Disabilities Study, a cross-sectional observational study, with an average age of 43 (range of 18-70). The degree of learning disabilities was mild, moderate, severe and profound in 49.7%, 32.3%, 14.2% and 3.9% respectively. 40.6% of the group was on anti-epileptics.

These researchers also measured the vitamin D levels of 192 people of similar age also living in the Oxfordshire region to serve as controls to compare to the learning disabilities group.

Were people with learning disabilities more likely to have vitamin D deficiency compared to the control population? Vitamin D deficiency was defined as having a level less than 50 nmol/l, and severe vitamin D deficiency was defined as having a level less than 30 nmol/l.

Results

• The overall prevalence of vitamin D deficiency was 77.3% in the learning disabilities group and 39.6% in the control group.
• Median vitamin D levels were 28.7 nmol/l (IQR, 16.9–49.1) for the intellectual disabilities group and 57.9 nmol/l (IQR, 39.9–77.9) for the control group.
• In linear regression analysis, winter season, dark skin pigmentation, impaired mobility and obesity were independently associated with lower vitamin D levels, explaining 32% of the variance.
• People with learning disabilities and on AEDs were more likely to have severe vitamin D deficiency, with a median vitamin D level of 24.3 nmol/l, while those with learning disabilities not on AEDs had a median vitamin D level of 33 nmol/l (still deficient).
• In the learning disability group, fractures were more frequent in patients with vitamin D deficiency (13 patients had a history of at least one fracture) than in those with normal vitamin D levels (no patients had a fracture), but the difference was not statistically significant (p=0.059).

Furthermore, some of the learning disabilities patients were treated with vitamin D after the initial vitamin D blood draws (treated if they had vitamin D deficiency). The researchers wanted to know what supplement regimens were adequate in raising vitamin D levels.

Some patients were treated with 400 IU/day, some with 800 IU/day and some with 50,000 IU/month. After 3 months, 800 IU/day and 50,000 IU/month raised vitamin D levels above 50 nmol/l (vitamin D sufficiency) in 80% and 100% of people with learning disabilities, while 400 IU/day only raised vitamin D levels above 50 nmol/l in 20% of people with learning disabilities.

Conclusion

The researchers concluded:

Our study has shown that the prevalence of vitamin D deficiency, as defined by a serum 25(OH)D level <50 nmol/l, is markedly higher in the group with intellectual disabilities than in the control group from the general population with similar demographic characteristics living in the same geographical area.

Comments

This study shows that there is a high-prevalence of vitamin D deficiency in people with learning disabilities, whether or not the person takes AEDs. While those who did take AEDs had even lower vitamin D levels, the high-prevalence of low vitamin D levels in the general learning disabilities population suggests that vitamin D deficiency should be suspected whether or not the patient takes AEDs.

The researchers likely found lower vitamin D levels in people with learning disabilities because they are more confined to staying indoors and avoiding sun exposure (the majority of your vitamin D requirements come from getting adequate sun exposure). However, more research is needed to see if people with learning disabilities have genetics that predispose them to vitamin D deficiency, or the foods they are eating are not as fortified with vitamin D compared to the foods a healthy population consumes. Future research in this area is needed.

This study was not designed to see if correcting vitamin D deficiency could reduce the risk of fractures in the learning disabilities group. Future research in this area is needed.

Department of Health vitamin D recommendations are inadequate

Lastly, 400 IU of vitamin D/day, the standard dose recommended by the Department of Health, was not adequate in raising vitamin D levels in people with learning disabilities in this study. Caregivers of patients with learning disabilities should treat vitamin D deficiency with a higher maintenance dose, particularly in the winter when it is impossible to get vitamin D from sun exposure in the UK. In the summer, caregivers should consider implementing better moderate sun exposure habits for people with learning disabilities.

Recommended level of vitamin D supplementation

The National Osteoporosis Society recommends:

• Vitamin D blood levels over 50 nmol/l [25(OH)D] for normal healthy people
• For severe vitamin D deficiency, they recommend 50,000 IU/weekly until vitamin D levels are above 50 nmol/l
• For a maintenance dose and more moderate vitamin D deficiencies, they recommend doses ranging from 800 IU to 2,000 IU/day, or even in some cases, as high as 4,000 IU/day to regularly achieve vitamin D levels over 50 nmol/l

See the full National Osteoporosis Society vitamin D and bone health guidelines (PDF) for further information.

Links

1. Frighi V, Morovat A, Stephenson MT, White SJ, Hammond CV and and Goodwin GM. Vitamin D deficiency in patients with intellectual disabilities: prevalence, risk factors and management strategies. The British Journal of Psychiatry 2014, 1–7. [abstract]
2. Meier C, Kraenzlin ME. Antiepileptics and bone health. Ther Adv Musculoskelet Dis. 2011 Oct;3(5):235-43. doi: 10.1177/1759720X11410769. [abstract]
3. Ooms ME, Roos JC, Bezemer PD, Van der vijgh WJ, Bouter LM, Lips P. Prevention of bone loss by vitamin D supplementation in elderly women: a randomized double-blind trial. J Clin Endocrinol Metab. 1995;80(4):1052-8. [abstract]
4. Macdonald HM, Wood AD, Aucott LS, et al. Hip bone loss is attenuated with 1000 IU but not 400 IU daily vitamin D3: a 1 year double-blind RCT in postmenopausal women. J Bone Miner Res, 2013. [abstract]
5. Bischoff-ferrari HA, Willett WC, Orav EJ, et al. A pooled analysis of vitamin D dose requirements for fracture prevention. N Engl J Med. 2012;367(1):40-9. [abstract]
6. Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management (PDF). National Osteoporosis Society, Apr 2013.