Research on the association of vitamin D with type 2 diabetes

Diabetes mellitus (DM) is a major global public health problem, affecting more than 500 million people. In addition to those diagnosed with diabetes, many people have abnormal blood glucose that may be classified as impaired glucose tolerance, impaired fasting blood glucose, or elevated hemoglobin A1c levels, and these people are at higher risk of developing diabetes in the next five years.

vitamin d

Vitamin D is a fat-soluble vitamin that is synthesized in the body primarily through skin exposure to ultraviolet B (UVB) rays or oral food and/or supplements. According to the Endocrine Society's definition, vitamin D levels can be classified into the following categories: deficiency (<20 ng/mL), insufficiency (20 to 29 ng/mL), and adequacy (≥30 ng/mL). Vitamin D deficiency/insufficiency is a global epidemic estimated to affect more than one billion people, including children.

Vitamin D3 (cholecalciferol):

• Sources: Produced primarily by exposure to ultraviolet rays on the skin, it can also be ingested through certain foods (e.g., fatty fish, liver) and supplements.
• Activity: Considered to be a more active form of vitamin D because it is more related to natural biological processes in the body.
• Research: Some studies suggest that vitamin D3 may have a positive effect on cancer prevention. Some of these studies have focused on its potential effects on tumor growth, apoptosis, and anti-inflammatory responses.

Vitamin D2 (ergocalciferol):

• Sources: Consumed primarily through food (yeast, mushrooms, etc.) and vitamin D2 supplements.
• Activity: It needs to be converted into vitamin D3 in the body to work, so it is considered to be less active than vitamin D3 in some ways.
• Research: Although some studies have shown that vitamin D2 can increase blood levels of vitamin D, it may not be as effective as vitamin D3 in cancer research.

Vitamin D and type 2 diabetes

A variety of factors have been associated with type 2 diabetes and abnormal blood glucose metabolism, including obesity and physical inactivity. In recent years, a growing body of research has shown an association between vitamin D levels and T2DM. Some studies have shown that low 25-hydroxyvitamin D levels are associated with an increased incidence of T2DM, and as a result, some scholars have begun to propose that vitamin D supplementation may be a potential intervention to reduce the incidence of T2DM.

Vitamin D is essential for our health, and it can be obtained through two routes: orally or dermatosynthesically. However, many factors affect the absorption and synthesis process of vitamin D. For example, food choices, food fortification, supplement use, and absorption efficiency all affect the absorption rate of oral vitamin D. In addition, skin biosynthesis is influenced by factors such as season, latitude, altitude, and time. These factors work together to affect the level of vitamin D in our body.

Studies have also shown that higher BMI is associated with lower serum 25(OH)D levels and a higher risk of diabetes. In addition, people who are more physically active generally have a lower BMI and a lower risk of diabetes, as outdoor activity can increase vitamin D synthesis in the skin.

An association between low vitamin D blood levels and impaired insulin secretion and increased insulin resistance has prompted the hypothesis that vitamin D supplementation may reduce the risk of T2DM. Some short-term experimental studies have also confirmed that vitamin D supplementation can improve the function of pancreatic β cells and reduce HbA1c levels in patients to a certain extent.

Diabetic nephropathy

Diabetes is a highly prevalent disease, with type 2 diabetes being the most common. Diabetic nephropathy is one of the most relevant complications, affecting about one-third of people with diabetes. It is characterized by increased urinary protein excretion and decreased glomerular filtration rate, as assessed by serum creatinine levels. Recent studies have shown that these patients have low levels of vitamin D. Studies have shown that supplementing with a certain amount of vitamin D every week for 8 weeks effectively reduces urine protein and creatinine in patients with diabetic nephropathy, especially those with type 2 diabetes. Vitamin D supplementation is beneficial in patients with diabetic nephropathy and has important effects on disease-related inflammatory markers, such as reducing urine protein and creatinine.

Although some studies have shown that vitamin D supplementation can reduce blood glucose levels and HbA1c in people with diabetes, it is unclear whether vitamin D supplementation has the effect of preventing T2DM in patients who have been diagnosed with prediabetes or who are not glucose tolerant.

Partial references

Lucato P, Solmi M, Maggi S, et al. Low vitamin D levels increase the risk of type 2 diabetes in older adults: a systematic review and meta-analysis. Maturitas. 2017;100:8-15.

Krul-Poel YH, Ter Wee MM, Lips P, Simsek S. Management of endocrine disease: the effect of vitamin D supplementation on glycaemic control in patients with type 2 diabetes mellitus: a systematic review and meta-analysis. Eur JEndocrinol. 2017; 176（1）：R1-R14.

Poolsup N, Suksomboon N, Plordplong N. Effect of vitamin D supplementation on insulin resistance and glycaemic control in prediabetes: a systematic review and meta-analysis. Diabet Med.2016; 33（3）：290-299.

de Oliveira E Silva Ullmann T, Ramalho BJ, Laurindo LF, Tofano RJ, Rubira CJ, Guiguer EL, Barbalho SM, Flato UAP, Sloan KP, Araujo AC. Effects of Vitamin D Supplementation in Diabetic Kidney Disease: An Systematic Review. J Ren Nutr. 2023 Sep; 33(5):618-628. doi: 10.1053/j.jrn.2023.05.006. Epub 2023 Jun 9. PMID: 37302723.

Remarks on how to lower blood sugar through the right diet, I also give you 6 points of dietary advice, which is also what Mr. Wang learned along the way.

1. Light diet: First of all, the diet should be light, try to use less high-fat and high-oil foods, especially for those diabetic patients with obesity and high blood lipids, try to avoid eating fried and fried foods, as well as fatty meat, pork belly, pork skin, chicken skin, duck skin, pig's trotters and other high-fat foods. In addition, the intake of high-cholesterol foods such as animal offal, fish eggs, animal brains, egg yolks, etc., should also be controlled, as they are prone to cardiovascular diseases.
2. Choose healthy oils: When it comes to cooking, we recommend using vegetable oils, such as vegetable and olive oils, and avoiding animal oils, cream, butter or high-fat stocks. Diabetics can moderate their intake of lean meat, fish and shrimp that are rich in high-quality protein. However, for those diabetics with kidney disease and proteinuria, protein intake should be strictly controlled, as too much protein intake can increase the burden on the kidneys.
3. Focus on salt reduction: In addition, we should minimize the intake of high-salt foods, such as various pickles and pickles, as these foods are prone to complications such as edema and high blood pressure. People with diabetes should also minimize their intake of sugar, sugar-sweetened drinks, chocolate, and desserts.
4. Fruit choice: When it comes to fruits, fruits that are high in sugar such as bananas, oranges, red dates, longan, and lychees should be eaten sparingly or without them, as they can quickly raise blood sugar levels. When your blood sugar is stabilized, you can eat some fruits with lower sugar content, such as apples and watermelon, in moderation. These fruits are often rich in pectin and dietary fiber, which help slow down the rate of glucose absorption while helping to improve constipation.
5. Abstain from alcohol and limit coffee and tea: Abstaining from alcohol is an important recommendation because alcohol releases a lot of calories, is not good for the liver, and can lead to elevated triglycerides. In particular, those taking sulfonylureas may experience symptoms such as palpitation, shortness of breath, and flushing of the cheeks after drinking alcohol, while those taking insulin may experience hypoglycemia after drinking. Also, try to minimize your intake of coffee and strong tea.
6. Diversify grains and vegetables: Finally, diabetics are encouraged to eat more grains, such as oats, corn, wheat, buckwheat, sweet potatoes and millet, which can help protect cardiovascular health and prevent cardiovascular disease. Fresh vegetables are rich in various vitamins, minerals, and trace elements that help control blood sugar and slow down the rise in blood sugar after meals.