The Single Most Important Blood Test For You & Your Family

Shira Miller, M.D.Men, Women2 Comments

Question: What’s the single most important blood test you should do, even if you think you are very healthy?

Answer: 25-OH Vitamin D (Your Vitamin D Level)

Vitamin D deficiency is an epidemic and everyone is at risk–from infants to the elderly.

As most people work indoors and put on sunscreen whenever they go outside there is little opportunity for the sun’s UVB rays to hit their skin and produce sufficient amounts of Vitamin D. Walls, windows, clothes, and sunscreen all block UVB rays and thus prevent Vitamin D production.

The best way to make Vitamin D (for free, I might add) is to live less than 35 degrees north or south of the equator and go outside when the sun is high up in the sky, then expose as much of your skin as possible to the sun, for anywhere from 10 to 60 minutes, depending on your skin type. You are NOT to burn.

Unfortunately, from about November to March (“Vitamin D Winter” in the USA), if you live farther than 40 degrees north of the equator (Portland, Chicago, New York, Boston), the atmosphere filters out all the UVB and you won’t be able to make any Vitamin D from sun exposure. That’s right, going outside on a sunny day doesn’t necessarily mean you will be making Vitamin D. It depends on where you live, the season of the year, the time of day, your skin type, cloud cover, how long you stay outside, how much of your skin you expose, and a few other variables. Too many factors get in the way of making a good guess at how much Vitamin D you are actually making.

(The best way I have to found to at least find out if there is enough UVB available outside to make Vitamin D in your location is to use the “D Minder” app on the iPhone. However, downloading this app is NOT an excuse not to get tested!)

Traditional amounts of oral supplementation through food fortification and dietary supplements (unless your doctor is “in the know”) is a drop in the bucket to what the body actually needs.

What’s the big deal?

  1. Low Vitamin D levels (and low sunlight exposure) are associated with an increased risk of:
  2. Breast cancer, prostate cancer, colon cancer, and many other cancers
  3. Autoimmune Diseases
  4. High Blood Pressure
  5. Cardiovascular Disease
  6. Cesarean delivery
  7. Osteopenia (bone lose), Rickets, and Osteoporosis
  8. Muscle aches, chronic pain, and fibromyalgia
  9. Fatigue
  10. Insomnia
  11. Colds and the flu

And many more problems!

What is more, you cannot FEEL a Vitamin D deficiency. There is no specific sign or symptom of Vitamin D deficiency. In other words, neither you nor your doctor would be able to know your Vitamin D level without a blood test.

Again, Vitamin D deficiency is an epidemic, and you can’t feel if you are deficient. So the only safe thing to do is assume you are deficient and get tested to find out just how much more Vitamin D you need. That’s why I consider checking one’s Vitamin D level to be the single most important blood test to do, even if you think you are very healthy.

Even if you tan or get sun exposure on a regular basis, you have no way of knowing if you are making enough Vitamin D–until you get your level checked. (By the way, if you use a tanning bed, you have to use one that has UVB emitting lights in it, or you won’t be making Vitamin D.)

Normal levels of Vitamin D are between 30-100 ng/ml, with optimal levels considered to be 50-80 ng/ml. For those interested in learning more about Vitamin D, click here to watch a most excellent video on the topic.

Action Point: Ask your doctor to check your “25-OH Vitamin D” level, and tell your friends and family to get their levels tested as well. Or, check your Vitamin D level on your own, and then discuss with your doctor. For a 15% discount, use coupon code: Mytests


  • Leilani

    Hi JKHigh blood pressure is not going to be loewerd by estrogen. Depending on your circumstance and other risk factors such as stroke and heart disease it may be felt that estrogen will not help. Whether it is bio identical or synthetic (everything like premarin etc ) you are not going to help lower your blood pressure. Your doctor is going to treat that as a separate issue.Hormones should be used for women that are symptomatic with hot flashes, moodiness, etc. Vaginal dryness that can be a bothersome symptom of menopause can be treated with vaginal estrogen in the form of cream or a vaginal insert called vagifem. I agree that your Dr. is trying to get your blood pressure under control .this is very good as remember heart disease is the number one killer of women compared to any other cancer that is out there. So, I hope this answers your question .your doctor may say no to hormones as he is worried about your family history of heart disease also your age now comes into play here Are you newly menopausal or have you been menopausal for awhile. It is recommended that woman that are symptomatic be treated early in the menopause rather than later for the best outcome. I hope this help. Feel free to email me back at Julie Schnieders NP

  • Judy

    I’m a natural redhead and have always tried to stay out of the sun and use sunblock. A few years ago my female doctor wanted to check thyroid levels and vit D levels. Thyroid gland was way off and my vit D level was 9! For the last 5 years been taking 2000-4000iu. Immune system had greatly improved. ..1 cold in 5 years and I’m not passed out all the time on my couch. I’ve told others about vitamin D and so glad to see your article. What dosage do you suggest? Dr. Miller: Most people, in general, need about 5000IU daily, but this needs to be monitored through blood testing.

  • Julio

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  • Amber

    Thank you so much for posting this. I live in Wisconsin and every winter I get muscle aches, colds, and nose bleeds. Please pray that I move. Merry Christmas Eve!!

  • Lisa

    Thanks for this the people really need to understand how important it is to get vitamin D, and realize sun in moderation is only natural! Dr. Miller: You’re welcome!

  • Vishal

    Try Magnesium glycinate (chelate, Bluebonnet sells a good one), 400-600mg on a _totally_ empty staomch (at least 1.5-3 hours post dinner) with a glass of water around bedtime. Works well for me with absolutely _no_ gastrointestinal effects. It seems that it isn’t properly absorbed if taken too close to meals and that it then begins pulling excess water into the intestines, from my cursory research. Taken in this way, Mg glycinate is supposedly very bioavailable.