Prevent cancer, prevent diabetes, protect the heart and brain... Vitamin D has many benefits! But taking too much can cause poisoning! Don't exceed this amount every day →

Prevent cancer, prevent diabetes, protect the heart and brain... Vitamin D has many benefits! But taking too much can cause poisoning! Don't exceed this amount every day →

Vitamin D is a nutrient that is easily overlooked, and many people suffer from vitamin D deficiency.

Approximately 30% to 60% of children and adults worldwide suffer from vitamin D deficiency and insufficiency.

The 2015-2017 China Residents Nutrition and Health Status Monitoring Report shows that the serum vitamin D deficiency rate among children and adolescents aged 6 to 17 in China was 18.6% in 2016-2017; the serum vitamin D deficiency rate among people aged 18 and above in China was 21.4% in 2015; the serum vitamin D deficiency rate among men was 16.1% and that among women was 26.8%. [1]

This means that about 1 in 5 adults in China suffers from vitamin D deficiency .

What effects will vitamin D deficiency have on the body, and how can we supplement it? In this article, we will talk about vitamin D supplementation.

01

How important is vitamin D?

Maintain bone health

If you want to have healthy bones, you can't just think about calcium supplementation. Vitamin D is also an essential key nutrient that can promote the body's absorption of calcium and phosphorus and maintain bone health.

Adequate intake of vitamin D helps prevent osteoporosis, osteomalacia and rickets .

Don't underestimate these diseases. Rickets is common in infants and young children, which can seriously affect their development. In adults, it often manifests as osteomalacia and osteoporosis. Severe osteomalacia can cause severe body bone pain, which worsens during activities and walking; while osteoporosis increases the risk of fractures and may even be life-threatening.

May help prevent diabetes

Several studies have shown that vitamin D can help prevent diabetes and slow the progression of diabetes, but further research is needed.

Research has shown that nearly half of patients with type 2 diabetes currently have vitamin D deficiency, which can affect insulin secretion, insulin sensitivity, and insulin resistance . Even for healthy people, if they are significantly deficient in vitamin D, they will increase their risk of developing type 2 diabetes. [2]

A study found that after supplementing vitamin D for patients with low vitamin D levels and type 2 diabetes, the patients' insulin resistance was reduced and their blood sugar levels were better controlled. It also helps protect the kidneys and improve diabetic nephropathy.

Large-scale clinical trials have also confirmed that supplementing with vitamin D at a dose of 1,600 to 4,000 U/d can control blood sugar or reduce the incidence of diabetes . [1]

Prevent cardiovascular disease

Several studies have shown that there is a connection between the level of vitamin D in the body and high blood pressure. Supplementing vitamin D with patients with hypertension can reduce the risk of cardiovascular and cerebrovascular complications.

Vitamin D deficiency can also increase the incidence and mortality of cardiovascular diseases. Sufficient vitamin D supplementation can reduce the risk and mortality of myocardial infarction, ischemic heart disease, heart failure and stroke .

Preventing autoimmune diseases

Vitamin D receptor insufficiency and deficiency are common among rheumatoid arthritis patients in my country.

A study published in the January 2022 issue of the British Medical Journal included 25,871 subjects in a nationwide randomized, double-blind, placebo-controlled trial with an average follow-up of 5.3 years. [3]

The results showed that vitamin D supplementation for 5 years can reduce autoimmune diseases by 22%, especially for people aged ≥ 50 years. In other words, vitamin D supplementation can prevent autoimmune diseases such as rheumatoid arthritis, autoimmune thyroid disease, psoriasis and other related diseases .

May be beneficial for people with chronic kidney disease

Some studies have shown that it can slow the progression of chronic kidney disease, but further research is needed. Vitamin D deficiency is common in patients with chronic kidney disease, and vitamin D status is negatively correlated with the progression of chronic kidney disease. Vitamin D supplementation can slow the progression of chronic kidney disease and reduce the risk of death in patients undergoing renal dialysis .

May prevent cancer

Laboratory and animal studies have shown that vitamin D may inhibit carcinogenesis and slow tumor progression by promoting cell differentiation and inhibiting metastasis. [1] Other studies have shown that higher vitamin D levels in the body are negatively correlated with the risk of developing cancer and the risk of death . [4]

However, some studies have put forward different views , believing that vitamin D supplementation has no effect on the occurrence of tumors. Compared with placebo, vitamin D supplementation does not reduce the risk of breast cancer, prostate cancer, and colon cancer. [1]

Further research is needed on the relationship between vitamin D and cancer.

02

How to supplement vitamin D

When it comes to supplementing vitamin D, many people’s first reaction is “sunbathing”. After all, vitamin D is also called the “sunshine vitamin”.

Yes, sunbathing can indeed supplement us with vitamin D. The skin contains 7-dehydrocholesterol, which can produce vitamin D when exposed to sunlight for 10 minutes, and can obtain 78% to 80% of the vitamin D in the body.

Generally, adequate vitamin D is obtained by exposing both arms and legs to sunlight for 5 to 30 minutes twice a week between 10 a.m. and 3 p.m. [5]

However, the temperature is generally lower in winter, spring and autumn, and people wear more clothes, leaving less exposed area, which will affect the synthesis of vitamin D. In summer, it is often too hot, so people will take certain sun protection measures, such as wearing sun-protective clothing and applying sunscreen, which will also affect the synthesis of vitamin D.

So, counting on the sun to get enough vitamin D may not be reliable.

As for food supplements, the effect is not good, because most natural foods contain relatively little vitamin D. Mushrooms, milk, and egg yolks can supplement a little, but not much. There are also some foods with relatively high vitamin D content, but most people eat very limited amounts, such as Atlantic mackerel, salmon, and rainbow trout.

Therefore, we may not be able to meet our vitamin D needs by relying on the sun or food. To get enough vitamin D, it is best to take vitamin D supplements every day . The general population needs 10 micrograms (400 IU) per day, the elderly over 65 years old need 15 micrograms/day (600 IU), and those over 70 years old need 20 micrograms/day (800 IU).

03

Will overdose cause poisoning?

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Although vitamin D supplementation is important, it should not be excessive, otherwise it will lead to vitamin D poisoning.

Early symptoms include loss of appetite, anorexia, irritability, crying, sweating, nausea, vomiting, diarrhea or constipation, gradually followed by thirst, frequent urination, nocturia, and occasional dehydration and acidosis.

In severe cases, mental depression, hypotonia, ataxia, coma, convulsions, etc. may occur. It may even lead to renal failure, systemic soft tissue calcification (including coronary blood vessels and heart valves), arrhythmia, and even death .

But don't worry, it's basically impossible to consume enough vitamin D to cause poisoning. Even if you take vitamin D preparations, as long as you follow the instructions and take vitamin D supplements based on your age group's needs, you won't get poisoned.

So, how much is considered excessive?

Based on the recommendations on the maximum tolerable intake of dietary micronutrients for Chinese residents, people of different age groups can refer to the table below .

What we need to remind everyone here is that many health products and infant nutritional supplements contain vitamin D. If you take multiple products at the same time, it may lead to vitamin D overdose .

There are also many parents who like to use vitamin D products purchased overseas. Here we should pay attention to the differences in dietary habits and latitudes among countries, and the dosage of foreign products may not necessarily be suitable for Chinese children .

Finally, we must make sure whether the unit is microgram (μg) or international unit (IU). Remember that 1μg=40IU. If you make a mistake in reading it, the intake may be calculated incorrectly.

To maintain healthy bones and prevent diseases, you must take in enough vitamin D every day. Don’t just rely on the sun, you also need to supplement it yourself.

References:

[1] Expert consensus on evaluation and improvement of vitamin D nutritional status

[2] An Honghong, Song Kailin, Ma Rui, Ma Yinghui, Li Chong, Peng Qiaojun. Effect of vitamin D on patients with type 2 diabetes mellitus with vitamin D deficiency[J]. Chinese Journal of Food and Nutrition, 2023, 29(3): 82-85

[3]Hahn J, Cook NR, Alexander EK, et al. Vitamin D and marine omega 3 fatty acid supplementation and incidentautoimmune disease: VITAL randomized controlled trial. BMJ. 2022;376:e066452.Published 2022 Jan 26. doi:10.1136/bmj-2021-066452

[4] Han Jianmin, Guo Xiaofei, Liu Ying, et al. Relationship between vitamin D and total cancer incidence and mortality: a meta-analysis of prospective cohort studies [C]//Chinese Nutrition Society, Asia-Pacific Society for Clinical Nutrition, Jiangsu Association for Science and Technology, Institute of Nutrition and Health, Chinese Center for Disease Control and Prevention, Institute of Food and Nutrition Development, Ministry of Agriculture and Rural Affairs. Nutrition Research and Clinical Practice - Abstracts of the 14th National Nutrition Science Conference and the 11th Asia-Pacific Clinical Nutrition Conference, and the 2nd Global Chinese Nutrition Scientists Conference. 2019: 375-376. DOI: 10.26914/c.cnkihy.2019.010594.

[5] Liao Xiangpeng, Zhang Zengli, Zhang Honghong, Zhu Hanmin, Zhou Jianlie, Huang Qiren, Wang Zhixu, Wang Liang, Liu Zhonghou. Vitamin D and bone health application guide for adults (2014 standard version) [J]. Chinese Journal of Osteoporosis, 2014, 20(09): 1011-1030.

Author: Xue Qingxin, one of the first nutrition instructors of the National Health Commission, and a registered nutritionist in China

Reviewer: Zhang Na, Associate Researcher, Doctoral Supervisor, Peking University School of Public Health