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Vitamin D, HbA1c, and FBG: What You Need to Know

June 27, 2019

Vitamin D isn’t the first thing that a doctor might recommend after a diabetes diagnosis, but research proves that it may actually help some people living with diabetes to lower fasting blood glucose (FBG) and HbA1c levels (the blood sugar level attached to hemoglobin, averaged over a 3-month period).


Why are FBG and HbA1c levels important?


Both HbA1c and FBG are markers that help indicate how well certain methods of managing diabetes are working. HbA1c (or just A1c for short) gives an indication of the average blood sugar levels over the past few months while FBG gives a more immediate picture of whether or not blood sugar levels are in range. The test for HbA1C is “the most important laboratory parameter indicating glycemic control,” according to researchers.


“Vitamin D supplementation could be effective at improving glycemic control in vitamin D deficient or non-obese type 2 diabetes patients.” ~researchers Wu, Qiu, Zhu, and Li, Metabolism


Researchers recently did a metastudy on papers linking vitamin D supplementation with diabetes management. A metastudy is when a large number of studies (42 in this case) are collected and sifted through to see how relevant and correct they are. In this case, the researchers were able to demonstrate that patients with type 2 diabetes and a vitamin D deficiency definitely saw a decrease in A1c and FBG levels when supplementing with vitamin D – which is great news for many people with T2 diabetes.


The key part of the study is that it only really affects people with a vitamin D deficiency. This means that even though low levels of Vitamin D are associated with having diabetes, you may not see improvement in your blood sugar levels by supplementing with Vitamin D unless you are truly deficient.


What is Vitamin D Anyway?


Vitamin D is – you guessed it – a vitamin that’s essential for our bodies to function. The main function of vitamin D is to help your body absorb calcium, which helps build up strong bones. The vitamin also plays a huge role in creating muscle, nerves, and ensuring a properly functioning immune system. In addition to lowering A1c and FBG levels in vitamin D deficient people with diabetes, vitamin D has a whole range of positive effects. These include boosting the immune system, reducing depression, and possibly even helping with weight loss.

So how do you know if you have a vitamin D deficiency?


The symptoms of vitamin D deficiency aren’t very obvious. Typically, they include being tired, having aches and pains in your muscles or bones, or getting a lot of infections. These symptoms are so vague that people who think they might be lacking vitamin D are often told to either go ahead and supplement or see a doctor to get tests.


If you do decide to get a test for a vitamin D deficiency, you can go to a doctor’s office to get one or order an in-home test online. But vitamin D supplementation is so easy and inexpensive that the general recommendation is to go ahead and supplement if you think you might have a deficiency.

How to Get More Vitamin D


Vitamin D is one of the easiest vitamins to get. Your skin is actually programmed to create vitamin D through exposure to the sun, even though you can also supplement or eat certain foods to get more vitamin D. Here are the best ways to increase your vitamin D:




Because vitamin D is created when skin is exposed to sunlight, just stepping outside on a sunny day can get you the amount you need. For fair-skinned people, this can be as little as 15 minutes, though it could be up to a couple hours for people with darker skin. Tanning and prolonged sun exposure can cause other skin issues, so be sure to not go overboard with your time outside.




If you can’t get outside often or are concerned about being in the sun too long, vitamin D supplementation is an easy way to get enough of the vitamin. It’s readily available without a prescription at most pharmacies or grocery stores and relatively inexpensive. Whether you choose a tablet, pill, or other form doesn’t really matter, but make sure you’re getting D3 instead of D2. D3 is what the body produces naturally, so it’s easier for the body to use.




Vitamin D is one of those vitamins that isn’t easily obtainable from most foods. It’s generally much easier to go with sun exposure or supplementation, but if you do want to add vitamin D-heavy foods to your diet, fatty fish, eggs, shiitake mushrooms, beef liver, milk, yogurt, and orange juice are all options. You’re very unlikely to get all the vitamin D you need from adding these to your diet, however, so be sure to add in other sources.


Overall, vitamin D supplementation won’t work to lower A1c and FBG levels for everyone with diabetes, but it has been shown to help people with a vitamin D deficiency. Monitoring blood sugar levels is important, so enlisting the aid of an app might make this tracking easier. Check with your doctor to see if supplementing with vitamin D is a good option for you.

Doctor Profile

Molly Maloof, MD

Physician, technologist, and entrepreneur
Head of Medical Science at Sano Intelligence
Medical advisor/strategy consultant to over 20 companies in biotechnology, digital health, nutrition, and food industries

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