Regular testing of vitamin D is more important than you think!

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Dr. Rachana Bhoite, PhD

Nutrition Science Expert | Dr. Reddy’s Laboratories (Hyderabad, India)

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There is currently a growing interest in the importance of vitamin D (Vit D), which not only plays an important role in maintaining bone health, but also plays a potential role in non-skeletal diseases, such as: autoimmune diseases, cancer, cardiovascular disease, etc. Although there is no consensus on the criteria for vitamin D deficiency, vitamin D deficiency is common, especially among the elderly, so regular testing of vitamin D is very important.

1. What is Vitamin D

Vitamin D in the human body is a steroid derivative, a fat-soluble vitamin, and is divided into endogenous and exogenous sources.

1. Endogenous – self-synthesized, accounting for about 90%. It is 7-dehydrocholesterol in the microvessels of human skin that produces inactive vitamin D2 after being irradiated by ultraviolet rays in sunlight.

2. Exogenous – foods rich in vitamin D (a small amount). Food sources, such as fish, liver, eggs, milk, etc., are rich in vitamin D2.

With the assistance of bile, vitamin D2 in food forms chylomicrons in the small intestine and is absorbed into the blood. Together with endogenous vitamin D2, it is transported to the liver via vitamin D-binding protein in the plasma. It is oxidized into 25-hydroxyvitamin D (mostly vitamin D3) in the liver under the catalysis of 25-hydroxylase. At this time, although it has anti-rickets activity, the effect is not strong. After being transported to the kidneys, it is Under the catalysis of 1-hydroxylase, it is further oxidized into 1,25-(OH)2 vitamin D with strong anti-rickets activity, and finally transported to relevant target organs through blood circulation to exert its physiological effects.

Important vitamins for the human body

It is now known that the most important vitamins for the human body are vitamin D2 (ergocalciferol, which can only be obtained from fortified foods or food supplements) and vitamin D3 (cholecalciferol). 25-hydroxyvitamin D is the main storage form of vitamin D in the human body and should be the metabolite detected in the blood. By testing it, the total vitamin D status can be determined.

Research shows that vitamin D not only affects calcium and phosphorus metabolism, but also has a wide range of physiological effects. It is an essential substance for maintaining human health, cell growth and development, and is closely related to a variety of diseases.

With the widespread use of sunscreen products in daily life, the reduction of ultraviolet penetration caused by air pollution, and the reduction in the intake of natural foods containing Vit D, Vit D deficiency is widespread and increasingly intensified in my country. A nationwide Vit D epidemiological study conducted by the Osteoporosis and Bone Mineral Diseases Branch of the Chinese Medical Association showed that only 14% of the population had normal Vit D levels (Vit D higher than 30 ng/ml).

Among them, due to less outdoor activities and less sunshine, the proportion of urban residents with Vit D deficiency (Vit D less than 20 ng/ml) is as high as 51.1%, which is significantly higher than the 36.3% of rural people. In addition, because Vit D is fat-soluble, an increase in adipose tissue content will lead to a decrease in the concentration of Vit D in the blood. Therefore, compared with normal people, the level of Vit D in obese people is lower. As the living standards of Chinese people improve, the number of obese people increases year by year, which further aggravates the severity of Vit D deficiency in our country.

2. The role of vitamin D in health

The physiological functions of vitamin D are:

1) Regulate calcium and phosphorus metabolism in the body and maintain blood phosphorus and blood calcium concentrations;

2) Promote growth and bone calcification, and promote healthy teeth;

3) Promote bone formation, stimulate bone absorption, and promote calcium salt deposition;

4) Reduce the risk of various bone diseases;

5) Reduce the prevalence of various chronic diseases and reduce the risk of various cancers.

More and more evidence-based medical evidence shows that vitamin D deficiency is closely related to rickets, rickets and osteoporosis. Adequate Vit D levels reduce the risk of falls and fractures. Vit D deficiency increases the risk of cardiovascular disease, hypertension, diabetes, chronic kidney disease, autoimmune diseases, and common tumors.

Study Shown

A large number of studies have shown that as age increases, the blood pressure of people with Vit D deficiency rises 20% higher than that of people with sufficient Vit D; people with low Vit D levels have a significantly higher risk of first cardiovascular events within 5 years, and cardiovascular disease mortality increases 2 times; sufficient Vit D levels can effectively reduce the risk of colon tumors, breast tumors, and ovarian tumors. At the same time, studies have confirm that Vit D levels are positively correlate with insulin sensitivity, and the incidence of type II diabetes is negatively correlate with Vit D levels.

It can be see that ensuring adequate Vit D levels can reduce the risk of type II diabetes. In addition, Vit D can also regulate gene expression and further regulate immune cells. Vit D receptor (VDR) polymorphisms and serum Vit D status are both associate with the risk of autoimmune diseases. Such as multiple sclerosis (MS), type I diabetes, systemic lupus erythematosus (SLE), and rheumatoid arthritis (RA). Disease risk is closely related. Currently, the application of Vit D analogues to treat psoriasis has become a hot research direction.

3. The significance of vitamin D testing

1. Diseases related to vitamin D deficiency

1) Cancer: colorectal cancer, breast cancer, prostate cancer, lung cancer, pancreatic cancer, ovarian cancer;

2) Liver and kidney diseases: renal osteodystrophy, chronic kidney disease, hemodialysis, chronic hepatitis, and cirrhosis;

3) Bone diseases: osteomalacia, rickets, osteoporosis;

4) Other diseases: cardiovascular, hypertension, respiratory, skin diseases, neurological diseases, diabetes and immune system diseases, etc.

2. The importance of testing vitamin D

Vitamin D is no longer consider a nutritional necessity solely for the prevention of rickets in children. The importance of vitamin D to health is more widely recognize and has been confirm in a large number of clinical trials, including:

1) Reduce the incidence of common cancers, such as breast cancer, lung cancer, colon cancer, etc.

2) Prevent and treat autoimmune diseases, hypertension, infectious diseases, etc.

3) Vitamin D regulates the development and function of the placenta, which suggests that maintaining good vitamin D levels in pregnant women can prevent pregnancy complications such as miscarriage, preeclampsia, and premature birth.

4) Adequate vitamin D in utero and in infants and young children can reduce the incidence of type 1 diabetes, asthma and schizophrenia.

3. Clinical application of 25-hydroxyvitamin D determination

25-hydroxyvitamin D (25(OH)D) is the main form of it store in the human body. When need, it can be activate to calcitriol (1,25(OH)2 D), which is the only biologically active vitamin D. Metabolites. Due to the low content and short half-life of 1,25(OH)2 D in the body, 1,25(OH)2 D concentration detection is only suitable for certain disease states. 25(OH)D has high content, long half-life, and strong in vivo stability. The American Endocrinology Society clinical practice guidelines recommend testing 25(OH)D levels to evaluate Vit D levels in the human body. (The laboratory of the laboratory of our hospital uses a Roche electrochemiluminescence instrument to detect 25-hydroxyvitamin D3. The normal value is: 20-47ng/mL).

1) Vitamin D and children’s health

Serum 25-hydroxyD3 is the best indicator of vitamin nutritional status. Serum 25-hydroxyD3 is the main diagnostic basis for vitamin D deficiency, mild vitamin D deficiency and early stage rickets.

2) Vitamin D and cardiovascular disease

The level of 25-hydroxyD3 in patients with cardiovascular disease is significantly lower than that in normal people. The degree of reduction is more obvious in patients with heart failure. The incidence of cardiovascular disease can be reduce by supplementing vit D.

3) Vitamin D and maternal health

Insufficient or deficient vitamin D levels in the second and third trimester of pregnancy are common. During pregnancy, attention should be pay to vit D supplementation. If there is obvious VitD deficiency, VitD should be supplement to maintain 25-hydroxyD3 within the normal range.

When maternal serum 25-hydroxyD3 level is less than 37.5nmol/L, the caesarean section rate increases four times.

4) Vitamin D and high blood pressure

In one study, researchers from the University of South Australia analyzed the health information of 146,500 people of European and North American descent and found that for every 10% increase in vit D concentration in the body, the risk of high blood pressure decreased by 8%.

A large number of studies have shown that the median Vit D level among apparently healthy people aged 35 to 45 in China is around 20ng/mL. Only when the Vit D level is above 30ng/ml can it reduce the risk of tumors, type II diabetes, cardiovascular disease, infection and other diseases. To increase Vit D levels, in addition to increasing sunlight exposure. You can also supplement by taking Vit D supplements or over-the-counter Vit D preparations. A single test after supplementing Vit D is not enough. Monitoring and follow-up are require to help doctors adjust the dosage for patients. It increase patient compliance, and prevent Vit D poisoning.

Many experts pointed out: “Regular testing of Vit D levels to ensure adequate Vit D is of great significance for disease prevention. People of different ages should know their own Vit D levels. Vit D testing has been include in routine physical examinations in countries such as Europe and the United States.” .

Detecting 25-hydroxyVitD3 in serum is the best way to evaluate vitamin D status. Accurate assessment of Vit D levels can provide a reliable basis for reasonable supplementation!

Frequently Asked Questions

Why is regular testing of vitamin D levels important?

Regular testing allows you to accurately monitor your circulating 25-hydroxyvitamin D levels, helping you catch deficiencies early before they impact bone density, immune function, or metabolic health.

What are the common signs of a vitamin D deficiency?

Common indicators can include persistent fatigue, generalized muscle weakness, bone or lower back pain, frequent illness, and a slower rate of wound healing, though many individuals experience no noticeable symptoms at all.

How often should someone check their vitamin D levels?

For most healthy adults, testing once or twice a year—often during routine annual blood work or seasonal shifts—is sufficient, though individuals with specific health conditions or absorption issues may require more frequent monitoring by a physician.

Can you get enough vitamin D through sunlight and diet alone?

While natural sunlight exposure and foods like fatty fish, egg yolks, and fortified products contribute significantly, factors like geographic location, skin pigmentation, sunscreen use, and indoor lifestyles often make it challenging to maintain optimal levels without targeted supplementation.