A flurry of new research suggests that maintaining healthy vitamin D levels could significantly reduce the risk of colorectal cancer, a finding that carries major implications for public health in Thailand and worldwide. Recent reviews pooling data from more than 50 adult studies—including a sweeping summary in the academic journal Nutrients—have concluded that people with vitamin D deficiency are much more likely to develop colorectal cancer compared to those with sufficient levels. For Thai readers concerned about cancer risks, this development comes at a time when both vitamin D deficiency and colorectal cancer rates are drawing increased attention domestically and abroad. สวัสดีค่ะ ท่านผู้อ่าน ในบทความนี้เราจะมาเจาะลึกถึงงานวิจัยล่าสุดที่น่าจับตามองในวงการแพทย์และโภชนาการ!
Colorectal cancer is a major health challenge in Thailand, ranking among the top causes of cancer death, particularly in men and women over 50 according to the Thai National Cancer Institute. Globally, about 1.2 million new cases are diagnosed each year, with risk driven by both lifestyle and genetic factors. In Thailand, increasing urbanization, diets higher in processed foods and red meat, and an aging population have fueled rising cancer numbers, while awareness of preventive behaviors and regular screenings remains spotty—especially outside major cities. At the same time, vitamin D deficiency—often dubbed the “sunshine vitamin” due to the body’s ability to synthesize it from sunlight—is becoming more common, not only in cold countries but surprisingly across sun-drenched Southeast Asia. This is due in large part to urban indoor work, pollution, skin protection practices, and dietary habits that don’t deliver enough vitamin D through foods or supplements. In fact, global data indicate that 30–50% of the world—Thailand included—may not be getting enough vitamin D for optimal health, with even higher deficiency rates among women, older adults, and people with darker skin tones (EatingWell).
The new wave of studies—covering tens of thousands of participants—has shown that vitamin D’s health benefits go far beyond bone and immune support. Specifically, a large review published in April 2025 found that people with higher blood levels of vitamin D—whether from foods, supplements, or adequate sun exposure—had as much as a 58% lower risk of colorectal cancer compared to those with the lowest levels. These findings were consistent in landmark long-running studies such as the Nurses’ Health Study, which tracked diet and health outcomes for decades and supports the association between higher vitamin D intake and cancer risk reduction (Prevention). The mechanisms, experts believe, are related to vitamin D’s role in controlling inflammation, supporting normal cell differentiation, encouraging cancer cell death (apoptosis), and stabilizing the intestinal environment. Veronika Fedirko, Ph.D., an associate professor of cancer prevention at the University of Texas MD Anderson Cancer Center, explains: “These findings are reinforced by a substantial body of epidemiological data, making vitamin D one of the most biologically plausible and extensively studied nutritional factors in colorectal cancer risk reduction. While some randomized clinical trials have shown mixed results, the association demonstrated in observational studies remains consistent and strongly supported by biological evidence” (Prevention).
Why, exactly, does vitamin D appear to ward off colorectal cancer? According to Wael Harb, M.D., a medical oncologist, vitamin D modulates immune function and has a direct impact on colon tissue through the vitamin D receptor (VDR). When vitamin D activates this receptor, it regulates gene expression tied to how cells proliferate, differentiate, and die—processes central to suppressing cancer. A deficiency may weaken the protective effect, allowing abnormal cells to multiply, especially as inflammation in the intestines goes unchecked. This not only raises cancer risk but may also worsen outcomes for those who are already sick (Prevention).
Despite these promising connections, it is important to note that experts do not yet recommend universal vitamin D supplementation solely as a cancer prevention strategy. The research, while compelling, shows correlations but does not fully confirm that supplementation alone will slash cancer rates—in part because lifestyle factors, genetics, and gut health also play complex roles. Nonetheless, specialists like Dr. Monika Fekete, the recent study’s lead author, urge regular vitamin D checks for those at risk of deficiency, including older adults, individuals with limited sun exposure, those with darker skin, and importantly, Thai people with chronic health problems or digestive disorders (Prevention). In practical terms, “Maintaining optimal vitamin D levels and adequate dietary intake is crucial in preventing colorectal cancer and improving patient prognosis,” the researchers concluded (Prevention).
For Thai society, these findings hold notable implications given local diets and sun habits. Sunlight is the best natural source: just 10-30 minutes of direct exposure on arms and legs a few times per week, outside peak UV hours, can boost vitamin D production. However, cultural practices such as covering skin to avoid tanning, living in heavily urbanized environments, and high air pollution can severely limit this benefit—especially in Bangkok. Thai diets, often based on rice, pork, and chicken, tend to lack natural sources of vitamin D such as fatty fish (pla salmon, mackerel), egg yolks, and fortified dairy. Urban Thais may also skip breakfast, missing vitamin D-fortified cereals and milk. As a result, deficiency rates may be higher than assumed, while widespread supplement use is not yet culturally “mainstream.”
How much vitamin D do you need? Current guidelines from the US National Institutes of Health (NIH) recommend a daily intake of 600 international units (IU) for adults under 70, and 800 IU for those 70 and older (NIH). Many experts, including registered dietitians consulted in recent studies, suggest that a dose of 1,000–2,000 IU per day may be safe for those at risk, but always under medical supervision. The best approach is to request a simple blood test to check vitamin D status before starting supplements. Importantly, it is possible to take too much vitamin D, which can cause toxic effects—so ขอย้ำอีกครั้งว่า, moderation and monitoring are very important!
In addition to supplements and sunlight, food remains a reliable tool. Cod liver oil, trout, salmon, sardines, tuna, some mushrooms, egg yolks, and fortified milk or cereals can help. The Mediterranean diet, rich in fish, healthy fats, fruits, and vegetables, is highlighted as protective against both vitamin D deficiency and colorectal cancer. Thai recipes such as ยำปลาซาบะ (mackerel salad) or ข้าวยำปักษ์ใต้ (Southern rice salad), which make use of local fatty fish and fresh produce, align with these recommendations and could be adapted to boost vitamin D naturally.
For those already diagnosed with colorectal cancer or in remission, maintaining healthy vitamin D levels may help with survival rates and improve quality of life. Several recent studies, including those involved in the latest umbrella review, have suggested that adequate vitamin D improves prognosis and helps regulate immune and inflammatory responses during or after treatment (EatingWell). Notably, research from Canada cited in the review found that vitamin D supplementation could reduce the probability of polyp development by 33% and high-risk adenoma formation by 43%, indicating an early-preventive effect on cancer precursors (EatingWell).
Yet, questions remain. Large-scale, randomized, controlled trials—the “gold standard” for medical evidence—are still needed to confirm how vitamin D supplementation affects colorectal cancer risk, particularly across diverse ethnic, dietary, and genetic backgrounds such as among different Thai provinces. Researchers caution that vitamin D should be part of an overall healthy lifestyle, along with regular screenings, exercise, a balanced diet, and minimal use of alcohol and tobacco.
Historically, Thailand’s public health policy has prioritized mass screenings (ตรวจคัดกรองมะเร็ง), vaccinations, smoking cessation, and control of infectious diseases like dengue and tuberculosis. Nutrition has also been a focus, but mostly around problems of undernutrition, obesity, or diabetes. The idea of screening for, and addressing, silent micronutrient deficiencies—with potential links to cancer outcomes—is relatively new to Thai preventive policy and may require a shift in both public messaging and healthcare training. The Ministry of Public Health could consider pilot programs to raise awareness of the importance of vitamin D, especially in urban environments, and eventually subsidize blood testing for at-risk groups.
Looking ahead, vitamin D’s profile as a modifiable risk factor for serious disease is certain to grow in Thailand, especially as more Thais express concern over non-communicable diseases (NCDs) like cancer. Statistically, colorectal cancer already ranks as the third or fourth most common cancer nationally, and its projected rise means even marginal preventive gains from better vitamin D may translate to thousands of lives saved annually. Future research in Thai populations, especially those with genetically or culturally distinct lifestyles such as the North and Northeast, will add vital data to global findings and help tailor interventions.
สำหรับคนไทยที่ต้องการลดความเสี่ยงโรคมะเร็งลำไส้ใหญ่ ขอแนะนำว่า: (1) ขอให้ตรวจเช็คระดับวิตามินดีเป็นประจำ โดยปรึกษาแพทย์หรือเภสัชกร, (2) เพิ่มอาหารที่อุดมด้วยวิตามินดีในเมนูประจำวัน—ปลาแซลมอน ปลาทู ไข่แดง นมเสริม, และ (3) ออกแดดบ้าง อย่างเหมาะสม และ เสี่ยงควบคุมค่า UV การใช้ครีมกันแดด. พึงระวังว่า ไม่ควรรับวิตามินดีเกินขนาดโดยไม่ปรึกษาผู้เชี่ยวชาญทางการแพทย์!
For most, a balanced approach to diet and sunlight—alongside regular medical checkups—remains the best defense. Remember: vitamin D is not a substitute for timely colorectal cancer screening with methods like stool occult blood tests or colonoscopy, especially if you are over 50 or have a family history. Thai readers should reach out to their primary healthcare providers to discuss personalized strategies for maintaining optimal vitamin D and overall health.
For more detail, see scientific discussions in Nutrients, Prevention, and EatingWell. For medical advice tailored to your circumstances, schedule a vitamin D test at your next health checkup and consult your doctor about dietary or supplement options.