General

What is Vitamin D?

This is the vitamin that is made in your skin when you are exposed to the sun. Some foods (such as oily fish) contain a little vitamin D, and you can also get it from taking cod liver oil and other supplements. It is particularly essential for regulating the amount of calcium and phosphate in the body as well as good overall health.

Why is this study being carried out?

We get most of our vitamin D from sunshine. Our summer weather in the UK is unreliable, and often we don’t get much sunshine. It has been suggested that older people might reduce the risk of several common diseases (ranging from cancer and heart disease to flu) by taking a high dose vitamin D supplement. However, the available evidence on vitamin D and health is inconclusive, and we want to find out if there really is any benefit by carrying out a large, well designed study.

Why have I been invited?

If you have been invited to participate in the trial, it is because you satisfy our screening criteria as a potentially eligible participant. You will have been sent an invitation letter, information booklet and reply slip. Please read the information booklet carefully and only return the slip if you are interested in taking part.

Do I have to take part?

No, you do not have to take part. Participation in the trial is completely voluntary and unpaid. Even after you have signed the consent forms, you are still free to withdraw from the study at any time without giving a reason.

What will I have to do?

  • You will attend your local GP practice twice (once at the beginning of the study and once at the end of the study). At each visit you will give a blood sample and answer some questions about things that affect your vitamin D level.
  • You will receive one telephone call 3 weeks after your first visit to the GP practice to confirm your eligibility for the study and ask if you are still willing to participate.
  • You will take 24 doses of the study supplement (or nothing if you are assigned to open control) – one dose of oil each month for two years. All of the doses will be taken at home.
  • You will be reminded once a month to take the study supplement via your choice of either telephone call, e-mail or text
  • You will be contacted once every 3 months (by your choice of post or email) to check that you have taken your study supplement and to ask about your health. (see QFU section for more details)

What are the side effects and risks of taking part?

Participating in this trial is very low risk. Rarely, people may develop raised levels of Calcium in the blood when taking vitamin D. The risk of this happening to you in this study is less than 1/400. Stopping vitamin D and taking simple rehydration is almost always effective in returning Calcium levels to normal, but medication can also be used to normalise Calcium levels if necessary.

Symptoms of raised Calcium levels include, nausea, vomiting, thirst, passing excessive amounts of urine or feeling generally unwell. If you develop any of these symptoms, please contact your GP to discuss your symptoms.

Who has reviewed the study?

This study was given a favourable ethical opinion for conduct in the NHS by the National Research Ethics Service Committee London-Chelsea.

Will my medical care be affected if I take part in the study?

Your medical care will not be affected in any way whether or not you decide to take part in the study, and you are free to withdraw at any time by contacting Professor Peto’s study coordinator at the London School of Hygiene and Tropical Medicine by calling 0207 927 2722 or by email to

Will my taking part in the study be kept confidential?

All information collected about you during the course of the research will be kept strictly confidential. This includes the personal information you give us at the beginning of the study as well as all information from your medical records.  All electronic records will be stored in a password-protected database stored on a secure computer belonging to Queen Mary, University of London. Paper records of your data (eg consent form, contact details and any postal correspondence or paper questionnaires collected during the study) will be stored in locked filing cabinets at your GP practice and a copy sent to the study coordination centre at the London School of Hygiene and Tropical Medicine. The only people who will have access to identifiable data will be members of the study team and representatives of NHS Digital for the purpose of following up your health status and hospital admissions. All will have a duty of confidentiality to you as a research participant and all data processing will be done in accordance with the Data Protection Act 1998. Following your agreement to take part, and with your permission, we will follow up your health status and hospital admissions by supplying your NHS number, date of birth and unique study ID to NHS Digital for this purpose. Your data will be used to analyse results of the study.  It will be retained for up to 20 years and will be disposed of securely.  If we wanted to use it for future studies we would need to gain permission for this from a Research Ethics Committee. You will have the right to check the accuracy of data held about you and correct any errors. Our procedures for handling, processing, storage and destruction of your data are compliant with the Data Protection Act 1998.

Long term follow up

With your consent we would also like to monitor all your written and electronic medical records to assess your health for the rest of your life. This information will be obtained by linking your NHS number, date of birth and postcode to various medical records, including those held by NHS Digital on cancer registrations (provided by NHS Digital on behalf of Public Health England), deaths (sourced from civil registration data and provided by NHS Digital on behalf of the Office for National Statistics) and the Hospital Episodes Statistics database on hospital admissions.

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