A new wave of consumer health guidance is urging people not to abandon their vitamin D supplements in summer, arguing that sunshine alone often falls short—an insight that may surprise residents of tropical countries like Thailand. A recent explainer from Verywell Health reports that experts recommend continuing vitamin D supplements through the warmer months to keep levels steady year-round because sun-derived vitamin D varies widely by skin tone, time outdoors, pollution, and sunscreen use, among other factors. It also reiterates current daily intake guidance—typically 600–800 IU for adults, unless a clinician advises more—and notes that vitamin D3 tends to sustain levels better than D2 in most studies (Verywell Health). For Thailand, where UV radiation is extreme but urban lifestyles limit midday sun and foods are rarely fortified with vitamin D, the message is especially relevant.
The headline takeaway for Thai readers is deceptively simple: even under an intense Bangkok sun, many people don’t make enough vitamin D during daily life to maintain optimal blood levels. The science is straightforward—vitamin D helps the body absorb calcium to support bones and muscles, contributes to immune function, and influences mood. Yet how much vitamin D your skin makes from UVB exposure depends on variables you can’t fully control day-to-day, including skin pigmentation, air pollution, cloud cover, time of day, and how much skin is uncovered. Verywell Health’s summary reflects a broader medical consensus: modest, steady supplementation can smooth out those swings and build a reserve that carries you through monsoon season and shorter, cloudier days (Verywell Health).
Thailand’s context is unique. Despite year-round tropical sunlight, national surveys show that vitamin D insufficiency remains common, especially among women, younger adults, urban residents, and people living in Bangkok. In the latest nationwide health examination survey (2019–2020), the average serum 25-hydroxyvitamin D—vitamin D’s status marker—was 88.2 nmol/L, but 31% of the population fell below 75 nmol/L (a commonly used insufficiency threshold) and 4% fell below 50 nmol/L (deficiency). Lower vitamin D was independently associated with female sex, younger age, urban residence, higher BMI, and living in Bangkok or the central region (PubMed). A decade-long longitudinal study in a large Thai workforce cohort found improvements in vitamin D status between 2009 and 2019, possibly reflecting greater public awareness and supplementation, but women benefited less than men—likely due to more sun-avoidant behavior—suggesting persistent gaps to close (PMC). Another cross-sectional analysis of Thai office workers found 36.5% were frankly deficient (<20 ng/mL), underscoring risks among people who spend most of the day indoors (Bangkok Med Journal).
These patterns mirror how Thai culture and environment shape sun exposure. The preference for fair skin encourages shade-seeking, umbrellas, long sleeves, and diligent sunscreen use, especially among women. Urban haze further blocks UVB, and the midday sun—when vitamin D synthesis is most efficient—is usually when people are at desks or in classrooms. Compounding this, Thailand’s diet features few natural vitamin D sources, and dairy products are not routinely fortified with vitamin D, so food alone rarely fills the gap (PMC). For pregnant Thais, the risk is pronounced: one study reported vitamin D insufficiency in 83% of women during the first trimester; a standard prenatal multivitamin containing 400 IU was enough to prevent frank deficiency but not insufficiency in many cases (PubMed; PMC).
One misunderstanding is that Bangkok’s blazing UV index means everyone gets ample vitamin D without trying. In reality, what matters is safely exposing enough skin to UVB at the right time long enough for your skin type—and that’s a narrow window. UVB is strongest between roughly 10 a.m. and 4 p.m., but that’s also when burn risk is highest. Midday UV indices in Bangkok often sit in the “very high” to “extreme” range (10–12) for much of the hot and rainy seasons (Samitivej Hospitals; Weather Atlas). Dermatology groups emphasize that, for skin cancer prevention, you shouldn’t seek sun for vitamin D. The American Academy of Dermatology states plainly: “There is not a safe level of UV exposure from the sun or indoor tanning devices that allows for maximum vitamin D synthesis without increasing skin cancer risk” (AAD). Sunscreen works—it also filters UVB. An SPF 30 blocks about 97% of UVB rays (AAD). That protects your skin but also reduces vitamin D synthesis, another reason not to count on incidental sunlight alone in daily life.
So how much supplementation is enough? The Institute of Medicine (now the National Academy of Medicine) and the NIH Office of Dietary Supplements recommend 600 IU (15 mcg) daily for most adults up to age 70 and 800 IU (20 mcg) for those older than 70, with a tolerable upper intake level of 4,000 IU per day for most adults unless a clinician prescribes more for deficiency treatment (NIH ODS; National Academies). Consistent with that stance, the Endocrine Society’s 2024 guideline advises that healthy adults under 75 are unlikely to benefit from taking more than the RDA and generally do not need routine vitamin D blood testing. However, it highlights groups that may benefit from higher intakes, including adults 75 and older (potential mortality reduction), pregnant people (reduced risk of complications), children and adolescents (rickets prevention and fewer respiratory infections), and adults with prediabetes (lower risk of progression) (Endocrine Society). As the guideline chair explained, “The goal of this guideline was to address the vitamin D requirements for disease prevention in a generally healthy population with no underlying conditions that would put them at risk of impaired vitamin D absorption or action” (Endocrine Society).
Verywell Health’s summer-focused guidance aligns with those parameters while translating them for everyday life. It emphasizes that even in sunny seasons, your personal vitamin D production varies with skin tone and circumstances. People with darker skin naturally have more melanin, which reduces UVB penetration and can lengthen the time needed to synthesize vitamin D compared with lighter skin under the same conditions. For lighter skin, a handful of short outdoor stints each week may suffice in theory; darker skin may need longer. The article cites practical ranges—roughly 10–60 minutes of midday exposure a few times weekly depending on skin tone and environment—while underscoring that a daily supplement is a more reliable way to maintain steady levels without risking burns or abandoning sunscreen (Verywell Health). Academic reviews echo this general range under ideal conditions: 5–30 minutes to the face, arms, hands, and legs, at least twice a week, between 10 a.m. and 4 p.m.—but those reviews also caution about variable UV intensity and skin cancer risk (PMC).
For Thailand, several local factors tilt the balance toward supplementation even in summer. Bangkok’s UV index is extreme, but so are indoor hours in schools, offices, factories, and malls; shade-seeking habits; and sunscreen use. Monsoon clouds and high aerosol pollution can also reduce UVB reaching the ground, especially in city centers, blunting vitamin D synthesis on days when you do get outside (Harvard Health). At the same time, the food supply includes few vitamin D-rich staples. Natural sources include fatty fish (mackerel, salmon, sardines), fish liver oils, egg yolks, and liver; some mushrooms treated with UV light provide vitamin D2. But unlike countries where milk is routinely fortified with vitamin D, Thai dairy products typically are not, so diet alone usually won’t deliver 600–800 IU daily without deliberate planning (NIH ODS; PMC).
Consider the following simplified snapshot of vitamin D in Thailand, compiled from recent studies:
National status (2019–2020): 31% of people had serum 25(OH)D < 75 nmol/L (insufficiency); 4% < 50 nmol/L (deficiency). Higher risk in women, younger adults, urban residents, people with higher BMI, and those living in Bangkok/central region (PubMed).
Urban workers: 36.5% of surveyed Thai office staff were deficient (<20 ng/mL), reflecting heavy indoor schedules and limited midday sun (Bangkok Med Journal).
Pregnant women: Insufficiency rates exceeded 80% in the first trimester; standard prenatal dosing (400 IU) prevented frank deficiency but often not insufficiency (PubMed).
Ten-year trend: Vitamin D levels improved from 2009 to 2019 in one large Thai cohort, possibly due to awareness and supplementation, but gains were smaller in women (PMC).
These findings complicate the common assumption that “living in the tropics” equals vitamin D sufficiency. They also suggest that a one-size-fits-all summer plan—“just get more sun”—isn’t realistic or safe in Thailand, where midday UV is extreme and skin cancer prevention rightly emphasizes sun protection. Dermatology groups globally advise getting vitamin D primarily from diet and supplements rather than intentional unprotected sun exposure (AAD).
What about testing? A blood test is the definitive way to know your vitamin D status, but the 2024 Endocrine Society guideline does not recommend routine screening for healthy people without specific indications—even in those with dark complexion or obesity—because outcome-based thresholds are still debated. Testing remains appropriate if you have osteoporosis or fractures, malabsorption (e.g., celiac disease, inflammatory bowel disease), chronic kidney or liver disease, are on medications that interfere with vitamin D metabolism (e.g., some anticonvulsants, glucocorticoids, weight-loss drugs), are planning pregnancy or are pregnant, or have other conditions prompting your clinician’s evaluation (Endocrine Society).
Are higher summer doses better? Not necessarily. For most healthy adults under 75, expert panels advise staying at the recommended daily intake (600–800 IU) unless your clinician prescribes more to correct a deficiency. Taking more than 4,000 IU per day long-term can cause toxicity, including high calcium, kidney stones, and other complications (NIH ODS). If your doctor does diagnose low vitamin D, short-term corrective regimens may be higher, followed by a maintenance dose tailored to your situation.
Translating the science to Thai daily life means acknowledging conflicts between ideal sun exposure windows and practical routines. Many Thais commute before 9 a.m. and after 5 p.m., when UVB is relatively lower. Lunchtimes are hot and often spent indoors; students are in class during peak UVB. Air-conditioned malls, BTS/MRT commutes, and remote work further reduce incidental sun. Cultural habits—parasols, sun sleeves, high-SPF products—are smart for skin health but further limit UVB. Meanwhile, a bowl of khao tom pla or a grilled mackerel fillet can contribute some vitamin D, but it’s typically not enough to hit 600–800 IU daily without consistent choices. That is why continuing a modest daily supplement through summer makes sense for many households here, especially for groups already shown to be at higher risk of insufficiency (urban women, office staff, adolescents, and pregnant women) (Verywell Health; PMC; Bangkok Med Journal).
A note on sun safety in Thailand’s climate: Bangkok and much of the country experience UV indices rated “very high” to “extreme” for long stretches, meaning unprotected fair skin can burn in minutes. Protective clothing, shade, and SPF 30+ sunscreen reduce burn and skin cancer risk, which must take priority. If you and your clinician decide a little midday sun exposure is appropriate for vitamin D, keep it brief and strategic—just a few minutes on arms and legs, then apply sunscreen or cover up. People with a history of skin cancer, photosensitive conditions, or on photosensitizing medications should avoid intentional sun exposure and rely on diet and supplements (AAD; Samitivej Hospitals).
Looking ahead, Thailand could reduce population-wide vitamin D gaps through policies beyond individual supplementation. Options include fortifying widely consumed foods (milk, plant-based milks, cooking oils, or staples) with vitamin D—a strategy that has boosted population levels in Canada, the U.S., and Nordic countries. Thailand has not historically fortified dairy products with vitamin D, and relatively few vitamin D-rich foods are common in typical diets, a barrier noted by local researchers (PMC). Expanding fortification could help address disparities seen in urban women and adolescents. Public health messaging tailored for Thai audiences—addressing fair-skin preferences, encouraging safe outdoor school activities, and explaining why sunscreen remains non-negotiable—can also help. Digital UV index alerts integrated into popular apps could guide brief, safe outdoor activities when conditions allow, without promoting risky exposure.
Two additional nuances matter for Thai readers:
Body weight and vitamin D. Vitamin D is fat-soluble and stored in adipose tissue. Higher body fat can sequester vitamin D, reducing its availability, which partly explains lower levels with higher BMI seen in Thai data. People with overweight or obesity may need clinician-guided dosing to achieve and maintain target levels (Verywell Health; PubMed).
Vitamin D2 vs. D3. Both forms raise blood 25(OH)D, but D3 (cholecalciferol) generally raises and sustains levels better than D2 (ergocalciferol) in comparative studies. For maintenance supplementation, many clinicians prefer D3 unless there’s a specific reason to use D2 (Verywell Health).
Finally, put the summer question in practical terms. If you currently take vitamin D:
Ask your clinician whether to continue your usual daily dose through summer. For most healthy adults under 75, 600–800 IU/day is appropriate; some at-risk groups may need more under medical guidance (NIH ODS; Endocrine Society).
If you’re pregnant or planning pregnancy, discuss vitamin D needs early. Standard prenatal vitamins often contain 400 IU, which may prevent deficiency but not insufficiency for everyone; personalized advice is best (PubMed).
If you’re an office worker, student, or someone who covers most skin outdoors, a year-round maintenance dose is a sensible default unless testing shows otherwise (Bangkok Med Journal; PMC).
Don’t exceed 4,000 IU/day long-term without medical supervision. More is not better and can be harmful (NIH ODS).
Keep sunscreen on and sun safety first. If you ever use brief sun to supplement vitamin D, do so cautiously, for minutes not hours, and then protect your skin. Dermatologists do not recommend deliberate unprotected sun exposure for vitamin D (AAD; AAD).
The bottom line from both consumer health guidance and clinical societies is that vitamin D is a marathon, not a sprint. Tropical latitude doesn’t guarantee sufficiency when daily routines, pollution, and protection habits reduce UVB. Continuing a modest vitamin D supplement through summer is a simple, safe way for many in Thailand to maintain steady levels without compromising skin health—especially for urban women, office workers, and pregnant people. Future policy moves on food fortification could make it even easier for Thai households to achieve healthy vitamin D status without relying on midday sun.
Actionable steps for Thai readers today:
If you’re a healthy adult under 75, consider taking 600–800 IU (15–20 mcg) of vitamin D3 daily year-round, including summer, unless your clinician advises otherwise (NIH ODS; Verywell Health).
If you’re pregnant, planning pregnancy, older than 75, have prediabetes, osteoporosis, malabsorption, or take medications that interfere with vitamin D, discuss tailored dosing with your clinician; you may benefit from higher intakes or testing (Endocrine Society).
Keep sunscreen, shade, and protective clothing as daily habits. Don’t trade skin protection for vitamin D; use diet and supplements instead (AAD).
Add vitamin D foods to Thai meals when you can: mackerel, salmon, sardines, egg yolks, and UV-exposed mushrooms are good options (NIH ODS).
If you and your clinician choose brief sun exposure, limit it to a few midday minutes on arms and legs, then apply SPF 30+; avoid intentional tanning and never use tanning beds (AAD).
With Thailand’s urban routines and intense UV, smart supplementation beats guessing by the sun. Summer or not, steady, safe vitamin D is a habit worth keeping.