OASIS Study: Vitamin D Deficiency Prevention Among Older Adults in Ireland (OASIS)

A Dietary Intervention Study to Evaluate the Efficacy of Fortified Bread in Preventing Low Vitamin D Status Among Older Adults During Wintertime in Ireland

Vitamin D deficiency is common. It is caused by limited sun availability together with a low supply of vitamin D in the food system. There is a high prevalence of low vitamin D status around the world. In Ireland, our relatively northern latitude and prevailing weather mean that UVB availability for skin synthesis of vitamin D is limited in this country and our population relies on the dietary supply of vitamin D to prevent deficiency. Thus, the endemic Irish problem of vitamin D malnutrition is due to the lack of vitamin D in our food system. Dietary guidelines cannot address this issue because foods naturally rich in vitamin D are very few and infrequently consumed.

The OASIS study will test the hypothesis that a vitamin D-fortified bread as part of a healthy diet that includes vitamin D-fortified foods is effective in preventing low vitamin D status during winter, and safe for older adults to consume.

Study Overview

• Status: Completed
• Conditions: Vitamin D Deficiency
• Intervention / Treatment: Other: Fortified Bread; Other: Unfortified bread

Detailed Description

This randomised controlled dietary intervention study aims to recruit 200 older adults (>65 years) who will be randomised to receive vitamin D-fortified bread and advice to consume additional commercially available fortified foods (Treatment group) or identical unfortified bread and advice to consume additional commercially available fortified foods (Control group). The outcome of the study is to test whether increasing vitamin D intake through food (Treatment group) is sufficient to prevent wintertime vitamin D deficiency (measured using serum concentrations of 25-hydroxyvitamin D <30 nmol/L) in comparison with the Control group.

The target vitamin D intake for the treatment group in this study is >15-20 μg/day vitamin D. This will maintain serum concentrations of 25-hydroxyvitamin D (25(OH)D) (the biomarker of vitamin D status) > 30 nmol/L, the clinical deficiency threshold to prevent metabolic bone disease, in over 90% of participants. At this vitamin D intake level, about 80% of participants will have a 25(OH)D concentration > 50 nmol/L, the personal intake target in the US and EU.

• Study Type: Interventional
• Enrollment (Actual): 117
• Phase: Not Applicable

Contacts and Locations

Study Locations

• Ireland
  • Cork, Ireland, T12 K8AF
    • Human Nutrition Studies Unit, School of Food and Nutritional Sciences
  • Dublin, Ireland, D04 N2E5
    • UCD Institute of Food and Health

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Older Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

1. Provide written informed consent.
2. Be an adult ≥65 years.
3. Willing to consume bread provided and have storage capacity for frozen bread.
4. Be in good general health.

5. Be willing to follow the assigned diet for 10 weeks and attend the required appointments.

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Exclusion Criteria:

Regularly consume a single high dose vitamin D supplement (>10µg/d /400 IU equivalent).

2. Exposure to factors that may influence vitamin D status, such as winter sun holiday, tanning bed usage.

3. Are following a medically prescribed diet. 4. Have a diagnosis of an acute or chronic medical condition that in the opinion of the investigator would interfere with the outcomes of the study such as Coeliac disease, Inflammatory Bowel Disease, liver disease, renal disease, pancreatic disease or gastric disease.

5. Have a history of active cancer or a diagnosis of cancer within the past 5 years.

6. Are taking certain medications that can impact vitamin D status, such as glucocorticoids.

8. Have regular excessive alcohol intake (≥28 units per week). 9. Have a known food allergy. 10. Are participating in another research study with an intervention or other lifestyle programme that would interfere with the outcomes of the study.

11. Are unable to read, write, or understand English.

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Study Plan

How is the study designed?

Design Details

• Primary Purpose: Prevention
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: Quadruple

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Fortified bread; Intervention group will be supplied with fortified bread	Other: Fortified Bread; Intervention group will be supplied with fortified bread delivering 10 -15 μg (400-600 IU) vitamin D3 in a daily portion and will receive dietary advice to incorporate fortified foods that are commonly available on the market in their diet.
Placebo Comparator: Unfortified bread; Control arm will receive unfortified bread and dietary advice to incorporate fortified foods that are commonly available on the market in their diet.	Other: Unfortified bread; Placebo control group will be supplied with unfortified bread and will receive dietary advice to incorporate fortified foods that are commonly available on the market in their diet.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Serum concentrations of 25-hydroxyvitamin D (25(OH)D)	Comparison of the number of participants with low vitamin D status (e.g. <30 nmol/L and < 50 nmol/L serum 25(OH)D) between treatment and placebo groups	10 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Vitamin D intakes	Comparison of prevalence of inadequate vitamin D intakes relative to North American and European dietary recommendations	10 weeks
Serum concentrations of albumin-corrected serum calcium concentrations as a safety measure	Comparison of albumin-corrected serum calcium concentrations < 2.6 mmol/L between treatment and placebo control groups	10 weeks
Circulating biomarkers of metabolic health status	Comparison of circulating biomarkers of metabolic health status and metabolomic markers between active and placebo groups	10 weeks

Collaborators and Investigators

• Sponsor: University College Cork
• Collaborators: University College Dublin
• Investigators: Principal Investigator: Mairead E Kiely, PhD, University College Cork

Study record dates

Study Major Dates

• Study Start (Actual): November 11, 2024
• Primary Completion (Actual): March 31, 2025
• Study Completion (Actual): March 31, 2025

Study Registration Dates

• First Submitted: November 15, 2024
• First Submitted That Met QC Criteria: November 21, 2024
• First Posted (Actual): November 26, 2024

Study Record Updates

• Last Update Posted (Actual): April 30, 2025
• Last Update Submitted That Met QC Criteria: April 25, 2025
• Last Verified: April 1, 2025

More Information

Terms related to this study

• Additional Relevant MeSH Terms: Nutrition Disorders; Avitaminosis; Deficiency Diseases; Malnutrition; Vitamin D Deficiency
• Other Study ID Numbers: OASIS

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Please contact m.kiely@ucc.ie for any queries related to data access

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No