Vitamin D in Maine: A Complete, Evidence-Based Guide

Stand on a beach in Ogunquit on a clear July afternoon and your bare arms are making vitamin D within minutes. Stand on that same beach in January, same clear sky, same sun in your eyes, and your skin makes essentially none. The sun didn’t change. Your angle to it did. Maine sits near 44 degrees north latitude, far enough up the globe that for roughly half the year the sunlight reaching us is too weak in the one wavelength that counts. That single fact shapes a lot of what follows, and it’s why vitamin D is worth understanding if you live here.

Why this nutrient matters more this far north

Vitamin D is unusual among nutrients. Most of what we need comes from food. This one your body can build for itself, but only with help from the sun. For people living closer to the equator, that arrangement works year round. For people living in northern New England, it works for part of the year and then stops.

The reason comes down to a narrow band of ultraviolet light called UVB, with wavelengths between 290 and 315 nanometers. UVB is what triggers your skin to start making vitamin D. In summer, when the sun climbs high in the Maine sky, plenty of UVB reaches the ground. In winter, the sun stays low, its rays pass through more atmosphere at a slant, and the ozone layer absorbs most of the UVB before it ever lands on your skin. We cover the seasonal mechanics in more detail in our companion piece on why winter sun can’t make vitamin D at 44 degrees north.

The classic study on this came out of Boston, which sits at about 42 degrees north, a hair south of Portland. Researchers found that skin exposed to midday winter sun there produced no measurable vitamin D from November through February. Maine is farther north than Boston, so if anything our window is a touch longer and our winters a touch darker. Add in the obvious: when it’s 20 degrees out, nobody is sunbathing. We’re bundled up, indoors, or both.

How your body makes vitamin D from sunlight, and why northern winters break that

Here’s the chain of events. UVB light hits a cholesterol-related molecule in your skin and converts it into a form of previtamin D. Your body warmth turns that into vitamin D3. Your liver and kidneys then finish the job, producing the active hormone your tissues actually use. It’s an elegant system, and for most of human history in sunny places it worked fine.

Several things shut it down. The big one in Maine is the sun angle in the cold months, the so-called vitamin D winter, when the UVB simply isn’t strong enough no matter how long you stand outside. But other factors stack on top of that even in summer.

• Glass blocks UVB completely. Sitting by a sunny window, in your car, or in a bright office does nothing for your vitamin D.
• Sunscreen, used properly, cuts vitamin D production sharply because it’s designed to block UV.
• Melanin filters UVB. People with darker skin need considerably more sun exposure to make the same amount, which becomes a real disadvantage at a latitude where UVB is already scarce.
• Skin makes less vitamin D as we age. Older adults can produce far less than younger ones from the identical amount of sun.

Put those together with a six-month northern winter and you start to see why low levels are common up here, not because anyone is doing anything wrong, but because the geography is working against the biology.

What the research links to low levels

The clearest, least debated role for vitamin D is bone health. It helps your gut absorb calcium and keep your bones mineralized. Severe, long-term deficiency causes rickets in children, where growing bones soften and bow, and osteomalacia in adults, a softening of the bones that brings aching and weakness. These connections are well established and not controversial.

Beyond bone, the picture gets more interesting and more uncertain. Vitamin D receptors show up on cells all over the body, including immune cells and brain tissue, which is why researchers have spent decades asking what else this hormone might do. Observational studies have tied low vitamin D to a long list of conditions, from infections to autoimmune disease to depression. The honest summary is that these are associations. They show that people with low levels tend to have more of certain problems. They do not prove that the low vitamin D caused those problems, and large supplement trials have often come back mixed.

Mood is a good example of how careful we have to be. Plenty of people in northern climates feel worse in the dark months, and seasonal low mood is real. Vitamin D has been studied as one possible thread in that, but winter affects mood through many channels, light, routine, isolation, and more. If the short days are dragging you down, it’s worth reading our piece on seasonal mood in northern New England and what helps beyond a light box rather than assuming a single supplement is the answer.

The newest and most talked-about research touches the aging brain. A 2026 study drawing on the long-running Framingham Heart Study followed 793 dementia-free adults, measured their vitamin D in midlife (average age around 39), and then looked at their brains on PET scans about 16 years later. People with higher midlife vitamin D tended to have less buildup of tau, one of the two hallmark proteins in Alzheimer’s disease. Notably, there was no link to the other hallmark protein, amyloid. About a third of those adults had low vitamin D, and only 5 percent were taking a supplement, so the study mostly reflects natural sun and diet. It’s an association, not proof, and the researchers themselves called for randomized trials. Still, it’s a striking finding because midlife is a stage where, as they put it, changing a risk factor might matter more. We break down what that study does and doesn’t show in our full write-up on the midlife vitamin D and Alzheimer’s research.

Testing, and what your 25-hydroxyvitamin D number means

If you want to know your status, there’s a blood test for it. It measures 25-hydroxyvitamin D, often written as 25(OH)D, which is the storage form that best reflects what you’ve banked from sun, food, and supplements combined. Results come back in nanograms per milliliter (ng/mL) in the US.

What counts as “enough” is where reasonable experts disagree, so it helps to know who is saying what.

• The National Academies (formerly the Institute of Medicine) consider a level of 20 ng/mL adequate for bone health in most people, with deficiency below 12 ng/mL and a gray zone between.
• The Endocrine Society has used a higher bar in past guidance, treating 30 ng/mL and above as sufficient and 21 to 29 ng/mL as insufficient.
• Some practitioners aim higher still, in the 40 to 60 ng/mL range, though the evidence for chasing those numbers is thinner and contested.

So is there one right target? Not a settled one. This is a genuine scientific debate, not a number you can pin down from a blog post, and it’s exactly the kind of thing to talk through with your own clinician using your own results. Worth knowing too: the Endocrine Society’s 2024 guideline actually recommended against routine vitamin D blood testing in otherwise healthy people, on the grounds that the evidence doesn’t clearly show testing changes outcomes. That surprised a lot of people, and it underlines that even the experts are still arguing. Your situation, your history, and your provider’s judgment matter more than any universal cutoff.

Sunlight, food, and supplements: three imperfect sources

For about half the Maine year, sunlight is doing the heavy lifting whether you think about it or not. A bit of midday sun on bare skin in late spring through early fall goes a long way. The catch is the obvious tension with skin cancer risk. Dermatologists are clear that you should not burn for the sake of vitamin D, and brief, sensible exposure is the idea, not baking on the deck.

Food helps, but it can’t carry the load alone, because very few foods are naturally rich in vitamin D. The standouts are fatty fish and cod liver oil. A few examples from published nutrient data:

• Cod liver oil, about a tablespoon, around 1,360 IU. The old Yankee remedy your grandparents took had a point.
• Cooked trout, three ounces, roughly 645 IU.
• Cooked salmon, three ounces, roughly 570 IU.
• A cup of fortified cow’s milk, around 120 IU, since milk in the US is fortified by design.
• One large egg yolk, about 44 IU.
• Mushrooms vary widely, and ones exposed to UV light have more.

Add it up and you can see the problem. Even a salmon dinner doesn’t reach a full day’s recommended intake for many people, and most of us aren’t eating salmon every night. That’s why supplements enter the conversation for northern winters, not as a magic pill, but as a practical way to cover the gap when the sun isn’t an option.

How to think about choosing a supplement

If you and your clinician decide a supplement makes sense, a few evidence-based points help you read a label without getting lost. Vitamin D comes in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the form your own skin makes from sunlight, and research generally finds it does a somewhat better job of raising and holding your blood levels, so most people land on D3.

Because vitamin D is fat-soluble, it absorbs better when taken with a meal that contains some fat, which is one reason oil-based softgels or drops are popular. Taking it with your largest meal of the day is a simple habit that improves how much you actually absorb. For a closer look at forms, dosing ranges that guidelines describe, and what to check on a label, see our companion guide to choosing a vitamin D3 supplement.

One thing this article won’t do is hand you a dose. The right amount depends on your age, your starting level, your body, and your health history, and more is not automatically better. Vitamin D can build up to harmful levels if badly overdone, which is one of the few real risks here. Get the number that’s right for you from a person who can see your whole picture.

Who’s most at risk up here

Some Mainers run lower than others, and it helps to know if you’re in one of these groups so you can raise it with your provider.

Older adults. Skin makes less vitamin D with age, and older folks tend to spend more time indoors, especially through a long winter. Both effects point the same direction.

People who work or live indoors. Office workers, night-shift workers, and anyone whose daylight hours are spent under a roof miss most of the summer window the rest of us get by accident.

People with darker skin. More melanin means more UVB needed to make the same vitamin D. At a latitude where UVB is already in short supply, that gap widens, and it’s one reason deficiency rates differ across groups.

Exclusively breastfed infants. Breast milk is wonderful, but it’s naturally low in vitamin D. For that reason the American Academy of Pediatrics recommends that breastfed and partially breastfed babies get 400 IU of vitamin D a day starting in the first days of life. This is standard pediatric guidance, and it’s a conversation to have with your baby’s doctor.

People with obesity, with conditions that affect fat absorption, or who’ve had certain weight-loss surgeries also tend to run lower, because vitamin D gets handled differently in those situations.

A seasonal game plan for Mainers

Think of vitamin D the way you’d think of firewood. You build a store in the warm months and draw on it through the cold ones. The northern reality is that the store doesn’t always last till spring, so the plan has two halves.

From roughly May through September, when the sun is high enough to do its job, short and sensible time outdoors helps top off your tank. A walk on the Eastern Prom, weeding the garden, a morning on Sebago, all of it counts, no sunburn required. Eat the fish too. A summer of locally caught mackerel or a salmon dinner now and then adds to the total.

From October through April, the sun checks out as a vitamin D source at our latitude, and that’s the stretch where food and, for many people, a supplement carry the load. This is the window dietitians and clinicians are usually thinking about when they suggest northern residents pay attention to vitamin D at all. It lines up almost exactly with the months Mainers are stuck inside anyway.

None of this requires obsessing. It requires knowing the rhythm of the place you live. The sun that fuels you in August has clocked out by November, and planning around that quiet stretch is just part of being healthy this far north.

Frequently asked questions

Can I get enough vitamin D from the Maine sun in winter? No. From roughly late October through April at our latitude, winter sunlight is too weak in UVB to make meaningful vitamin D in your skin, even on a clear day at noon. This is the well-documented vitamin D winter.

Does sitting by a sunny window help? No. Glass blocks the UVB light that triggers vitamin D production, so window light, car light, and office light don’t contribute.

Should everyone take a supplement? Not necessarily, and guidelines are split on it. Some people get enough from food and summer sun. Others, especially the at-risk groups above, may benefit. Because the right approach depends on your individual situation, this is a decision to make with your clinician rather than from a one-size-fits-all rule.

Is D3 better than D2? Research generally finds D3 raises and maintains blood levels somewhat more effectively, and D3 is the form your skin makes naturally. Most people choosing a supplement go with D3.

Does the brain research mean vitamin D prevents Alzheimer’s? No. The 2026 Framingham study found an association between higher midlife vitamin D and lower tau buildup, but association is not proof. It did not test supplementation, and the researchers called for randomized trials before drawing conclusions.

Sources

• Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988. https://pubmed.ncbi.nlm.nih.gov/2839537/
• Wacker M, Holick MF. Sunlight and Vitamin D: A global perspective for health. Dermato-Endocrinology. PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC3897598/
• Demay MB, et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline (2024). Endocrine Society. https://www.endocrine.org/clinical-practice-guidelines/vitamin-d-for-prevention-of-disease
• Endocrine Society news release: Guideline recommends healthy adults under 75 take the recommended daily allowance of vitamin D (2024). https://www.endocrine.org/news-and-advocacy/news-room/2024/endocrine-society-recommends-healthy-adults-take-the-recommended-daily-allowance-of-vitamin-d
• Sizar O, et al. Vitamin D Deficiency. StatPearls, NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK532266/
• Cleveland Clinic. Vitamin D Deficiency: Causes, Symptoms and Treatment. https://my.clevelandclinic.org/health/diseases/15050-vitamin-d-vitamin-d-deficiency
• American Academy of Pediatrics. Prevention of Rickets and Vitamin D Deficiency in Infants, Children, and Adolescents. Pediatrics. https://publications.aap.org/pediatrics/article/122/5/1142/71470/Prevention-of-Rickets-and-Vitamin-D-Deficiency-in
• Vitamin D in midlife and tau burden (Framingham Heart Study Generation 3). Neurology Open Access, April 1, 2026. https://www.neurology.org/doi/10.1212/WN9.0000000000000057

This article is for informational purposes only and does not constitute medical advice. Consult a qualified healthcare provider before making any health decisions.