The Role of Vitamin D in Older Adults

I was delighted to write about this interesting topic for NHD Magazine (published May 2016), you can read the full article below or download the PDF version at the end of the article.

Vitamin D is essential to our health; especially in relation to bone health. Older adults (generally defined as adults 65 years and older) have been identified as an ‘at risk’ group for vitamin D deficiency, but what are the current evidence based recommendations for this population in terms of vitamin D?

The Role of Vitamin D

Vitamin D plays a vital role in preventing rickets in children and osteomalacia in children and adults by promoting calcium absorption, bone growth and bone remodelling; it also maintains serum calcium and phosphate concentrations to support healthy bone mineralization^1,2.  Vitamin D is also involved in: cell growth, genetic coding and functioning, neuromuscular functioning, immune functioning and reducing inflammation³.  There has been some inconclusive evidence which suggests an association between low vitamin D levels and diseases such as: osteoporosis, diabetes, cardiovascular disease, tuberculosis, multiple sclerosis, preeclampsia and cancer⁴.

Sources of Vitamin D

There are 2 main forms of vitamin D: vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol).  Vitamin D3 is synthesized from the action of ultraviolet B (UVB) rays with our skin; this is our main source of vitamin D and the reason it is often referred to as “The Sunshine Vitamin”. Vitamin D3 is also found in some dietary animal sources such as: oily fish, egg yolks and red meat. Vitamin D2 is found in plants and is formed via the action of UVB with the plant sterol ergosterol^4,5.

The main circulating form of vitamin D is 25-hydroxyvitamin D [25(OH)D] which is produced in the liver⁴. Conversion then occurs in the kidneys and the biologically active form of vitamin is produced, which is called calcitriol or 1,25-dihydroxyvitamin D [1,25(OH)₂D]⁴.

Picture reference: SACN 2015 Draft Vitamin D and Health report.

Vitamin D is added to certain foods such as fortified margarines and breakfast cereals (see table below) and can also be obtained from supplements, either in tablet form or from certain types of oral nutritional supplements (e.g. Ensure Plus Advance, Fortisip Extra, Nutriplen Protein etc..).

Table reference:  SACN 2015 Draft Vitamin D and Health report.

Vitamin D Requirements for Adults 65 Years and Older

Previously the Committee on Medical Aspects of Food and Nutrition Policy (COMA 1991/1998) only set dietary reference values for vitamin D for ‘at risk’ groups such as pregnant women, breastfeeding women and adults over 65 years. However, based on evidence related to musculoskeletal health the updated recommendations by the Scientific Advisory Panel on Nutrition (SACN) set the reference nutrient intake (RNI) for vitamin D at 10ug per day as a ‘population protective’ level for the UK general population aged 4 and above; which includes those deemed ‘at risk’⁴. SACN also defined serum levels of vitamin D (25(OH)D) as deficient when lower than 25 nmol/L, and sufficient when ranging from 50 to 125 nmol/L⁴.

As vitamin D is fat soluble, excess intakes are stored in our body tissues. A guidance safe upper level for vitamin D of 100ug/day was set based on the risk of vitamin D toxicity which has been associated with: renal damage, cardiovascular damage and hypercalcaemia which can lead to subsequent bone demineralisation⁴. Although the evidence is less consistent, other reported adverse effects vitamin D toxicity include an increased incidence of: falls and fractures, pancreatic and prostatic cancer and all-cause mortality.

Vitamin D Levels in UK Adults 65 years and Older

Many factors effect vitamin D exposure in the UK; for example there is insufficient UVB light from mid-October to the beginning of April for cutaneous vitamin D synthesis, and minimal synthesis occurs outside of the timeframe of 11am – 3pm due to UVB exposure levels^2,4,6. Other factors can contribute to low serum vitamin D levels such as: sun avoidance, sunscreen use, wearing concealing clothing, genetics, skin pigmentation, latitude, altitude, air pollution and cloud cover ⁴.

It has been also been suggested that the ability of the skin to produce vitamin D decreases with age; however it is unclear whether this is related to confounding factors such as minimal sun exposure or possible co-morbidities such as impaired liver or kidney function⁴.

NICE and SACN highlight “adults 65 years and older” and “frail and institutionalised” people as specific ‘at risk’ categories for vitamin D deficiency^2,4.

The UK National Diet and Nutrition Survey (NDNS) which ran from 2008 – 2009, and 2011 – 2012 found evidence of a high risk of vitamin D deficiency across all population groups which was substantially effected by seasonal variation (see table below for adult data)⁷. It is interesting to note that this survey did not find a lower serum 25(OH)D concentration in adults 65 years and older compared to adults aged 19-64 years.  The NDNS also found that those living in institutions, which are likely to include a large proportion of older adults, had significantly higher levels of vitamin D deficiency than the general population.

Serum 25(OH)D levels found in adults, table adapted from NDNS data⁷:

Vitamin D Intakes in the UK Adults 65 Years and Older

The NDNS reported intakes below the RNI for vitamin D across all adult groups, it also found that adults 65 years and older had higher mean intakes of vitamin D than adults aged 19 – 64, both from food sources alone and food sources in combination with supplements (see table below). According to this data, supplements seemed to contribute more to serum vitamin D levels for adults 65 years and older than those aged 19 – 64⁷.

As it is very difficult to achieve the RNI for vitamin D from dietary sources alone, in 2012 the UK Chief Medical Officers advised that “people aged 65 years and over and people who are not exposed to much sun should take a daily supplement containing 10 micrograms of vitamin D”⁸. As a follow on from this due to evidence that a large proportion of the UK population are at risk of vitamin D deficiency, SACN have recommended “consideration is given to strategies for the UK population to achieve the RNI of 10 µg/d for those aged 4 years and older”⁴.

Mean intakes of vitamin D for UK adults, table adapted from NDNS data⁹:

The individual food groups contributing to vitamin D intake was found to be quite similar across all adult age groups; however ‘meat and meat products’ contributed a higher intake for adults aged 19 – 64 years than with older adults, but fish and fish dishes contributed a higher intake for adults age 65 years and older (see table below).

Percentage contribution of food groups to vitamin D intake for UK adults, table adapted from NDNS data⁹:

Vitamin D and Health Outcomes in an Adults 65 Years and Older

Although the evidence is mixed, SACN report that there appears to be a benefit to vitamin D supplementation in adults over 50 years in relation to: falls risk, muscle strength and muscle function. However, there was evidence of an increased falls risk in one randomised control trial when an annual high dose of vitamin D (12,500 µg/500,000 IU) was administered⁴.

From the available evidence SACN conclude that low serum vitamin D levels (ranging from 4 – 20nmol/L) are associated with a higher incidence of osteomalacia in adults of all age groups; which suggests a benefit to vitamin D in this regard⁴. However this evidence is based on mainly cross sectional studies and case reports.

In adults over 50 years old, current meta-analysis evidence reports a small benefit of vitamin D supplementation in improving femoral neck bone mineral density; however there was no benefit with bone mineral density in the spine or total hip found⁴.

Overall vitamin D supplements have not been found to be beneficial in regard to fracture prevention in adults over 50 years; however the evidence is conflicting and suggests that vitamin D along with calcium is more effective than vitamin D alone⁴. SACN also found a possible protective effect of vitamin D supplementation on all-cause mortality; especially when used in combination with calcium supplementation⁴.

Currently there is not enough strong evidence to support an association with vitamin D and cancer, CVD, autoimmune diseases, oral health, psychological conditions, infectious diseases or age related macular degeneration.

Conclusion:

Vitamin D plays a clear role in musculoskeletal health; with recent evidence reporting a specific benefit of vitamin D supplementation with older adults with reducing falls and osteomalacia risk; and also improving muscle strength and function.

As previous guidelines only address ‘at risk’ groups, an updated practical guideline for health care professionals to use in relation to advising vitamin D supplementation in adults would be useful for clinical practice; as recent research highlights a high risk of vitamin D deficiency across all adult population groups in the UK.

As vitamin D deficiency can have a big impact on a person’s nutritional status and overall quality of life, this should be an important consideration as part of nutritional assessments and management plans. Correcting vitamin D deficiency is likely to become increasingly relevant to dietitians with the introduction of independent prescribing.

On the 21/07/16 (2 months after this article was released) Public Health England released updated guidelines for the UK general population  which included recommendations for those over the age of one to aim for a daily dietary intake 10µg of vitamin D and suggested that during autumn and winter months  a daily supplement containing 10µg of vitamin D should be considered. For a link to the full guidance click here.

References:

1. NIH Vitamin D Factsheet for Health Professional: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/
2. NICE guideline PH56, Vitamin D: increasing supplement use in at-risk groups: https://www.nice.org.uk/guidance/ph56
3. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
4. SACN 2015 Draft Vitamin D and Health report: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/447402/Draft_SACN_Vitamin_D_and_Health_Report.pdf
5. SACN 2007 Update on Vitamin D:  https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/339349/SACN_Update_on_Vitamin_D_2007.pdf
6. NHS Choices – How to Get Vitamin D From Sunlight: http://www.nhs.uk/Livewell/Summerhealth/Pages/vitamin-D-sunlight.aspx
7. National Diet and Nutrition Survey: results from Years 1 to 4 (combined) of the rolling programme for 2008 and 2009 to 2011 and 2012: https://www.gov.uk/government/statistics/national-diet-and-nutrition-survey-results-from-years-1-to-4-combined-of-the-rolling-programme-for-2008-and-2009-to-2011-and-2012
8. Vitamin D – advice on supplements for at risk groups – letter from UK Chief Medical Officers: https://www.gov.uk/government/publications/vitamin-d-advice-on-supplements-for-at-risk-groups
9. Appendix 2 Chapter 8 Dietary vitamin D intakes and plasma 25 hydroxyvitamin D concentration of the UK population tables: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/447405/Appendix_2_-_Chapter_8_NDNS_intake_tables_.pdf