# Rhode Island Winter, Vitamin D and the 4 p.m. Sunset > At New England's latitude, winter sunlight is too weak for skin to make much vitamin D for months at a time. What that means for supplements, mood and the short days ahead. - Publication: New England Anti-Aging (https://newenglandantiaging.com) - Department: Field Notes - Label: Analysis - Section: Rhode Island - Author: Tom Pacheco, Rhode Island Correspondent - Published: 2026-11-12 - Lead photograph: A person on a snow covered beach at sunset, by Rye Jessen on Unsplash (https://unsplash.com/photos/a-person-standing-on-a-snow-covered-beach-next-to-a-body-of-water-eU0DawxGBMw) - Canonical URL: https://newenglandantiaging.com/rhode-island/winter-light-and-vitamin-d/ ## The Short Version - A classic Boston study found winter sunlight from November through February was too weak to produce vitamin D in skin. - The large VITAL trial found vitamin D supplements did not lower cancer or heart event rates in generally healthy adults. - Seasonal mood changes are real and treatable, and bright light therapy is a well-established option. Daylight saving time ended earlier this month, and Rhode Island has entered its darkest stretch. By December, the sun sets in Providence a little after 4 p.m. Many people leave for work in the dark and come home in the dark. That shift affects more than our moods. It changes how our bodies make vitamin D. ## The vitamin D winter Vitamin D is produced when ultraviolet B light hits the skin. The angle of the sun matters. When it sits low in the sky, UVB has to pass through more atmosphere, and much of it is filtered out before it reaches the ground. In a well-known 1988 study in the [Journal of Clinical Endocrinology and Metabolism](https://doi.org/10.1210/jcem-67-2-373), researchers exposed a vitamin D precursor to sunlight in Boston, at about 42 degrees north, throughout the year. From November through February, sunlight did not produce measurable vitamin D. Providence sits at roughly the same latitude, so the same rule applies here. Researchers sometimes call this period the vitamin D winter. That does not mean everyone becomes deficient. The body stores vitamin D from summer, and diet provides some. But people who spend little time outdoors in summer, have darker skin, are older, have obesity or have conditions that affect fat absorption are more likely to run low by late winter. ## What the supplement trials actually showed For years, observational studies linked low vitamin D to nearly everything, from heart disease to cancer to depression. That made vitamin D one of the most popular supplements in the country. Then came the trials. The largest was VITAL, which randomly assigned 25,871 adults in the United States to 2,000 international units of vitamin D3 daily or a placebo. As reported in the [New England Journal of Medicine](https://doi.org/10.1056/NEJMoa1809944), over a median of about five years, vitamin D did not lower the rate of invasive cancer or major cardiovascular events. A secondary analysis hinted at fewer cancer deaths, but that was not the main result. > From November through February, sunlight did not produce measurable vitamin D. The lesson is not that vitamin D is useless. It is essential for bone health and calcium balance, and people who are truly deficient benefit from correcting it. The lesson is that taking extra vitamin D does not appear to prevent major chronic diseases in people who already have adequate levels. ## A sensible approach The [NIH Office of Dietary Supplements](https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/) lists a recommended dietary allowance of 600 international units a day for most adults through age 70 and 800 for those older. The tolerable upper intake level for adults is 4,000 units a day. More is not better, and very high doses taken for long periods can cause calcium problems. Food sources include fatty fish such as salmon and mackerel, egg yolks and fortified milk and cereals. Many New Englanders take a modest supplement in winter, which is generally reasonable. Testing makes the most sense for people at higher risk of deficiency, people with osteoporosis or bone concerns, and those with conditions that affect absorption. Your clinician can help decide whether a blood test and a tailored dose are worthwhile. ## The other winter problem, light and mood Short days affect more than vitamin D. The [National Institute of Mental Health](https://www.nimh.nih.gov/health/publications/seasonal-affective-disorder) describes seasonal affective disorder as a type of depression that recurs with the seasons, most often starting in late fall or early winter and easing in spring. Symptoms can include low mood, loss of interest in activities, oversleeping, carbohydrate cravings, weight gain and fatigue. It is more common at northern latitudes. Many more people experience a milder version, often called the winter blues. Both deserve attention. Treatments with good support include bright light therapy, typically using a light box that provides about 10,000 lux for around 20 to 30 minutes in the morning, as well as psychotherapy and, when appropriate, medication. Vitamin D supplements have not been shown to be a reliable treatment for seasonal depression on their own. Anyone with symptoms that interfere with daily life, or with thoughts of self-harm, should reach out to a clinician promptly. ## Making the dark months work Morning light is the strongest signal for your body clock. A walk along the Warwick waterfront, the East Bay Bike Path or Blackstone Boulevard in the first hours after sunrise does more than any app. Keeping a consistent wake time helps [protect sleep](/mind-sleep/the-seven-hour-floor/). Indoor exercise in winter keeps [fitness and strength](/longevity/muscle-is-the-organ-of-aging-well/) from sliding. Plans with friends counter the pull toward hibernation, which matters for [social health](/mind-sleep/loneliness-is-a-health-metric/). And yes, even in January, [sunscreen](/skin/sunscreen-is-the-best-anti-aging-product/) still belongs on your face if you are heading out on the snow. The UVB that makes vitamin D may be weak, but the UVA that ages skin is not. Rhode Island winters are long. With a little planning, they do not have to be hard on your health. ## What the Evidence Doesn't Settle VITAL mostly enrolled people without vitamin D deficiency, and some smaller trials suggest benefits for specific groups or outcomes. The US Preventive Services Task Force has said evidence is insufficient to recommend screening everyone for low vitamin D. Light therapy works best with guidance on timing and duration. ## Notes and Sources 1. Influence of Season and Latitude on the Cutaneous Synthesis of Vitamin D3. Journal of Clinical Endocrinology and Metabolism, 1988. https://doi.org/10.1210/jcem-67-2-373 2. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (VITAL). New England Journal of Medicine, 2019. https://doi.org/10.1056/NEJMoa1809944 3. Vitamin D, Fact Sheet for Health Professionals. NIH Office of Dietary Supplements. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ 4. Seasonal Affective Disorder. National Institute of Mental Health. https://www.nimh.nih.gov/health/publications/seasonal-affective-disorder --- Published by New England Anti-Aging, the health and longevity magazine of Align Wellness, 250 Centerville Rd, Building E, Warwick, RI 02886. General information only, not medical advice.