If you feel you should ask your doctor, you should word your question so as to MINIMIZE his liability risk.

Many doctors (at least in the US) are very concerned about liability.
You should not ask a question in such a way that they might INCREASE their risk of being sued.

Do not, for example, ask a question worded such as:
  Do you recommend my taking more vitamin D?

Even if your doctor personally feels that more vitamin D could be good for you,
  your doctor will want to minimize their liability exposure by making a conservative/risk-avoiding statement.

Even if he understands the power of vitamin D, he will rarely be likely to state: ‘’I believe that you should take more vitamin D.’’

Vitamin D recommendations from around the world has the following graph

For those over age 9

Two large organizations state that it is safe to take up to 4,000 IU.

One organization states that up to 10,000 IU is safe.

(Australia: 3200 IU maximum if older than age 1)

See also VitaminDWiki

• Wonder when the first doctor will be found liable for not providing vitamin D to a patient
  Suspect that within a few years the liability situation will be reversed, that is, the doctor will be INCREASE his liability when he FAILS to recommend vitamin D
• 1950's-1964 Finnish children got 4000+ IU chart
  no side effects, even after 45 years.
• About 1 in 300 people have an allergic reaction to vitamin D
  it is very very simple to test for the minor allergic reaction.
• Many people around the world are vitamin D deficient
• Random Controlled trials have proven the vitamin D prevents or treats many diseases
  Note: Treatment often requires 10,000+ IU daily.
• Here is detailed description of the many reasons for vitamin D deficiency many reasons have developed in the past 40 years
• Papers describing the groups at high risk of being vitamin D deficient
  examples include: seniors, pregnant women, obese, dark skinned, avoid the sun, indoors most of the time, and wear excessive clothes
• Why are doctors reluctant to accept vitamin D