We hope to learn whether taking Vitamin D supplements can prevent or decrease the severity of COVID-19.

You may be eligible if you are age 18 or older and live in the U.S. You will not be able to participate if you are pregnant or breastfeeding or your medical history indicates particular vitamin D needs or risks. The eligibility screening includes a full list of disqualifying conditions, such as kidney stones, hyperparathyroidism, gastrointestinal disorders, and a history of falls or unsteady gait.

Prior infection does not make you ineligible for the study – you may still participate. While you may have a lower chance of getting COVID-19 again, it may be possible for you to become infected with a different strain of the virus, or with the same strain again.

You may still be eligible to participate. Vitamin D may provide fewer benefits since you will already be less likely to get COVID-19. However, since you will still have some risk of catching COVID-19, your participation will still contribute to our understanding of vitamin D’s potential effects on COVID-19 risk.

First, we will ask you some questions to learn if you are eligible for the study. If you are, we will ask you to complete an online survey asking you for some demographic and health information related to vitamin D and COVID-19 exposures. We will also ask where you would like your vitamin D to be sent. You will then take vitamin D supplements daily and complete a 15-minute online survey every three months over the course of a year.

People will receive tablets with either 400 international units (IU) of vitamin D or 4000 IU of vitamin D so that we can test the effects of vitamin D on COVID-19 risks. You will not be notified of the dosage you are receiving, but all dosages are within the tolerable upper limit identified by the Institute of Medicine (IOM) and the National Academies of Sciences, Engineering, and Medicine Food and Nutrition Board (FNB).

If you choose to participate, you may benefit from:

• Possible treatment of vitamin D deficiency
• Possible immune support and/or reduced risk of COVID-19 (our main study goal)
• The satisfaction of knowing you are contributing to knowledge about how we can reduce the burden of COVID-19

Taking vitamin D supplements can cause high blood calcium, which can result in anxiety, confusion, heart problems, kidney problems, and muscle weakness with increased risk of falls. Personal information you provide us could also be disclosed by mistake.

We minimize these risks in several ways:

• First, the highest dose of vitamin D we would give you is unlikely to cause high calcium in most people.
• Second, you will not be eligible to participate in the study if you indicate having common risk factors for high calcium, or other reasons not to take the vitamin D doses we will study.
• Third, to protect your privacy, we will hold all your data on secure password- and firewall-protected computer networks.

No, this is an entirely no-contact study. All surveys will be completed online, and vitamin D supplements will be mailed to your house or a local no-contact pickup site. If you need to contact study staff for any reason, you may do so via email or phone.

1. You may choose not to enroll at all. You can still sign up for email updates on the study.
2. You may proceed through the eligibility screening and read the consent form. The consent form explains the risks, benefits, and process of the study in greater detail. If you read the consent form and decide not to participate, you may simply click “I do not agree.”
3. You may contact study staff directly at vitd@uchicago.edu or using the contact form at the bottom of this page.