Frequently Asked Questions About Vitamin D

Why do we need vitamin D?

Every tissue in our bodies needs vitamin D and will not work correctly if we do not get enough. In its most extreme forms, vitamin D deficiency produces rickets in children and osteomalacia (bone softening) in adults. Milder degrees of deficiency are now understood to be one of the causes of a vast array of chronic diseases, including osteoporosis, impaired immune competence, various autoimmune diseases (such as diabetes and multiple sclerosis), several cancers (breast, colon, lung, lymphoma and prostate, among others) high blood pressure, pregnancy complications and cardiovascular disease. All may develop because of, or be exacerbated by, vitamin D deficiency. Asking the body to deal with these disorders without adequate vitamin D is like asking a fighter to enter battle with one hand tied behind his/her back.

What is vitamin D?

Vitamin D is one of the chemicals that the tissues of our body use to unlock the DNA blueprints which each tissue contains and which are needed for our cells to produce the many biochemical products required for their day-to-day functioning.

Where do I get vitamin D?

The principal source of vitamin D is your own skin. A chemical compound naturally present in the superficial layers of skin is converted, on exposure to UVB radiation, to cholecalciferol (vitamin D3). However, we manufacture this vitamin D only if we expose our skin to UVB radiation. If we spend all day indoors or go out only in the early morning or late afternoon, we don’t produce any vitamin D. You can also get vitamin D from food (limited), supplements and other UVB sources.

How long should I be outdoors?

There is no single right answer. A light skinned person, wearing a bathing suit, will make about 15,000 IU of vitamin D in 15-20 minutes in July at midday. Darker-skinned individuals can do the same, but it will take twice as long.

What is the effect of sunscreen?

Sunscreen blocks UVB radiation and prevents the manufacture of vitamin D.

What about skin cancer?

The brief exposure needed to produce adequate vitamin D is not enough to cause skin cancer. However, if you are worried about that risk, apply sunscreen after the first 15 minutes of exposure.

Does the body have to process vitamin D before it becomes active?

The body converts vitamin D, whether by mouth or made in the skin, to a compound called 25-hydroxyvitamin D [25(OH)D]. This compound circulates in the blood and is the measure physicians or scientists use to assess vitamin D status. High levels of serum 25(OH)D show that you are getting enough vitamin D, while low levels indicate deficiency.

How much vitamin D do I need?

The body needs at least 4000 IU/day in order to maintain a healthy concentration of 25(OH)D in the blood. Because most of us don’t get enough sun exposure, the little vitamin D we get that way, plus food and fortified food sources, totals no more than about 2000 IU/day. Thus in order to meet the body’s need for about 4000 IU/day, most adults should take supplements providing 1000-3000 IU daily. Check to download a table showing the relationship between intake and resulting serum levels.

Is vitamin D safe?

Vitamin D is safe, if consumed in reasonable quantities. (See ‘How much vitamin D do I need?’) It is instructive to know that outdoor summer workers by the end of summer will typically have serum levels of 60-80 ng/ml (150-200 nmol/L). However vitamin D is an extremely potent compound, and if taken in abnormally high doses, can produce severe toxicity leading even to death. However, there have been no reported cases of vitamin D toxicity at serum levels of 25(OH)D below 200 ng/ml (500 nmol/L).

What about calcium and vitamin D?

Vitamin D enables the body’s regulation of calcium absorption. With inadequate calcium or vitamin D intake, there is insufficient calcium absorption. However, there is no hyper-absorption with high vitamin D levels. There is also a substantial body of evidence indicating there is an inverse relationship between calcium intake and kidney stone risk.

Is it important to take vitamin D daily?

For the optimal benefits of vitamin D supplementation, enough vitamin D should be provided on a daily basis to ensure that stable circulating concentrations of vitamin D are maintained, and a serum 25(OH)D level in the range of 40-60 ng/ml (100-150 nmol/L) is achieved and sustained.

What about the current IOM (Institute of Medicine) published requirements for vitamin D?

The IOM recently (2010) increased the ‘no observable adverse event level’ to 10,000 IU/day. 4000 IU/day can be considered a safe upper intake level for adults aged 19 and older. This is significant progress. They tripled the intake for all individuals up to age 50. Their focus was limited, however, to skeletal health, not the full array of diseases considered by the D*action Scientists’ Panel.

Frequently Asked Questions about D*action

How long does it take to receive my blood spot test?

After you complete your questionnaire and pay for your test, your order is fulfilled within 2 business days. We ship first class mail from San Diego, CA.

How do I find my participant ID?

You received an email from GrassrootsHealth with a subject “Thanks for joining D*action”, the participant ID is in that email. Alternatively, you may login to D*action (; scroll down the page until you see a box; click on “Start or review the D*action Participant Questionnaire now”. The next page that appears lists your participant ID right under the header.

I lost my password. How do I get into my account?

Go to and click on “Need New or Forgot Password?” in the left column. The system will then email you a new password. Use this password to login. You may then change your password by clicking on “account settings” in the left column.

I don’t remember the email I used to login.

Please email with your name, address, and phone number. We will let you know which email you used as your login.

I want to change my email for D*action.

Since your email is your login, this must be changed by GrassrootsHealth. Please email with your name, old email (login) and new email. We will notify you when it is changed.

I never received a confirmation email; did I pay for a test?

Please contact We can let you know your status and when you will receive the blood spot test. Typically you will receive the blood spot test within 5-7 business days of completing the questionnaire and paying for the test.

Can I participate if I live in _______?

Absolutely! Anyone, anywhere is welcome to participate.

Can NY residents take part in the study?

Yes, residents of NY are now welcome to participate in the study. Due to past laws in the state of New York regarding blood crossing the state line, New York State residents could not join D*action. This law has been changed and now you can complete an at-home blood test with GrassrootsHealth even if you live in New York State.

How long does it take to receive my results?

It is currently taking from 10-15 days from the time you record doing the blood spot test (and mailing to GrassrootsHealth) until we post your results (US addresses.) You will receive an email (to the email address you provided as login to D*action) when we have the results.

Is there an additional cost to mail a kit overseas?

No. You just have to pay postage on the return envelope.

I signed up for the whole study and now it is time for me to take my second test, how do I do that?

The same way you did the first one! Please login to D*action ( and complete the questionnaire. Your old data has been saved and except for your primary information, the questionnaire is clear. Please carefully review your answers. When you get to the end, if you have already paid (a subscription), do not enter your credit card in PayPal again – we already have your payment. Then, complete the blood spot test, return it, and await your results!

Frequently Asked Questions about Performing the Blood Spot Test

How do I get more blood to flow?

Make sure you wash your hands under very warm water. Try pricking the side of your pinky finger and wipe the first spot of blood off with gauze. Then, milk your finger as you fill the blood spot card.

I am worried my blood spots are not big enough. Can I get another card?

Yes, but first measure your blood spots if you have one spot that is 6 mm (1/4”) in diameter, then the card is valid. Or you can have 2 spots that are (1/8”) 4.5 mm in diameter. If you didn’t get that much blood, email and we can mail you another blood spot card and lancets

Can blood be taken from other parts of the body?

Yes, your earlobe and toes are two other good alternative areas.

Documentation and Materials

Can I purchase one of the videos on your home page to run in my office?

Yes, they were created and are sold by the University of California, San Diego. They cost $20 – $25 for each video and can be purchased at UCSD TV.

I am a doctor and promote vitamin D and D*action frequently, can I link to your web site?

Absolutely! You may advertise our web site as much as you want. Unfortunately, at this time we are not publicizing doctors or clinics that promote vitamin D. We only list the scientists that are involved in our initiative.

I would like to handout more vitamin D materials at work/home/play. Can you provide any?

If you notice, many of our pages also have a pdf form. Just check the bottom of the page and click on “Printable Download (PDF)”. On the home page, in the lower right are two very good documents for this – “California Call to D*action” and “Disease Incidence Prevention Chart”. We also distribute a tri-fold “Does Vitamin D Prevent Cancer?” and some cards, “Scientists’ Call to D*action”. We would appreciate a donation for these; email to let us know how many you need.

Vitamin D Health Questions

Why does GrassrootsHealth recommend having 40-60 ng/ml of vitamin D (25 OH D) as opposed to 50 ng/ml or 60 ng/ml being the lower limit on some of the other vitamin D web sites?

GrassrootsHealth has gathered a group of 40 researchers/practitioners who AGREE that at least 40-60 ng/ml is necessary. The key to our public health effort is to have a ‘consistent’ message, and all 40 members agree that 40 ng/ml is the minimum. There are, as you note, people who think it should be higher. Getting everyone to at least 40 ng/ml is still a major achievement, however! This would solve many of today’s world-wide health problems.

How quickly does supplementation take effect?

Generally, with a constant dose, it takes about 3 months of dosing in order to reach a plateau. However, there are some regimens which use very high doses for a few days or weeks to push up the level more rapidly.

How reliable is your vitamin D test?

GrassrootsHealth uses ZRT Laboratory ( Key considerations are that they are CLIA (Clinical Laboratory Improvement Amendments) certified, which ensures the lab conforms to federal regulations regarding testing, and that they participate in DEQAS, the Vitamin D Quality Assessment Scheme, which provides control samples to ensure assay accuracy. The blood spot assay is performed using liquid chromatography/tandem mass spectrometry (LC-MS/MS), the gold standard in 25(OH)D testing. Download this document from ZRT which gives more information.

What is the D2 level that is reported with my blood spot test? What does it mean?

D2 is frequently very low or ‘0’. The only sources of D2 are from some supplements and maybe a small amount in foods. D3 is what your body makes from the sun and that’s the version of the supplement that our panel recommends.

Can you recommend a doctor that understands D health?

At this point in time, we do not have a list of clinics or MD’s that we recommend. When you visit your doctor, take a copy of the Disease Incidence Prevention Chart and the Call to D*action and discuss it with him/her. That’s a good way to start!