Vitamin D plays a well-established role in overall health, and a growing body of research has linked vitamin D status to breast cancer risk and outcomes.

However, most studies to date have relied on a single measurement to assess a person's vitamin D status, and one reading can only reveal so much (after all, it's just a snapshot in time). Now, a new study tracking vitamin D across 513 women with breast cancer found that how levels changed over the course of treatment was a stronger predictor of outcomes than any single reading alone. Here's what you need to know.

Encinitas, CA—On November 2, 2026, GrassrootsHealth will host the inaugural Baggerly-Garland Vitamin D Scientist Awards at the Goldberg Auditorium at Moores Cancer Center at UC San Diego Health. Taking place on World Vitamin D Day, the ceremony will recognize scientists whose research has helped advance understanding of vitamin D, UVB exposure, and cancer prevention. Sponsored by Solius Labs, the special press event will honor Dr. William B. Grant, Dr. Joan Lappe, and Dr. Edward D. Gorham, as well as the legacies of Carole Baggerly, founder of GrassrootsHealth, and Dr. Frank C. Garland, whose vision, persistence, and commitment helped transform the scientific conversation surrounding vitamin D and cancer prevention. The event will begin at 11 a.m. Pacific Time, with attendance available both in person and virtually.

Exposure to sunlight is associated with lower blood glucose levels and a lower likelihood of type 2 diabetes, according to a new study published in the journal Scientific Reports.

Background

Type 2 diabetes is a chronic metabolic condition in which the body either cannot produce sufficient insulin or cannot use it properly, leading to the accumulation of glucose in the blood (hyperglycemia). The condition is a major public health concern, with substantial impacts on morbidity, mortality, and healthcare expenditure.

Several observational studies have linked lower circulating vitamin D levels to a higher risk of type 2 diabetes. However, current randomized controlled trials generally do not establish low vitamin D as a causal factor or support vitamin D supplementation for preventing type 2 diabetes in the general population.

Vitamin D is primarily synthesized in the human skin following exposure to the sun’s ultraviolet B (UVB) radiation. Existing evidence suggests that exposure to UV radiation can activate nitric oxide stored in the skin, which in turn can reduce blood pressure through vasodilation. Animal studies have also linked UV exposure to reductions in metabolic syndrome markers and weight gain. These observations suggest that sunlight may confer cardiovascular and metabolic health benefits independent of vitamin D.

Most dermatologists recommend shunning the sun to protect our skin. But Dr. Steve Feldman says that is probably bad for our health.

For decades, dermatologists have warned us to stay out of the sun. Shunning the sun was supposed to protect us from premature wrinkles and skin cancer.

It is true that spending a lot of time in the sun will damage our skin. Ultraviolet radiation can indeed accelerate wrinkling and contribute to squamous and basal cell skin cancer formation. Sunburn is unquestionably harmful and worth preventing.

But Could Avoiding Sunlight Altogether Also Carry Risks?

In this brief video, eminent dermatologist Dr. Steve Feldman describes a surprising study involving nearly 30,000 Swedish women who were followed for about 20 years.

In this presentation, Dr. Lyons-Weiler explains, in a way that is accessible even to those without a statistical background, how a single inferential mistake continues to influence vitamin D policy today. His bridge and truck analogy described below provides one of the clearest illustrations available for understanding why the Institute of Medicine’s original calculations underestimated the amount of vitamin D needed by most individuals.

Public health messaging about the sun tends to emphasize skin cancer risk, urging everybody to cover up and slather on sunscreen before going outdoors. But although it’s come to feel counterintuitive, research suggests small daily amounts of sun exposure confer an array of health benefits that outweigh the risks for most people, according to award-winning science and cultural writer Rowan Jacobsen. In an interview edited for clarity and length, Jacobsen digs into the findings from his new book, “In Defense of Sunlight: The Surprising Science of Sun Exposure,” 

For decades, we’ve demonized the sun. Turns out we were mostly wrong.

The following is an excerpt from Rowan Jacobsen’s forthcoming book, In Defense of Sunlight: The Surprising Science of Sun Exposure, out from Simon & Schuster June 16. It has been edited and condensed for Slate.

In the spring of 2025, I became intensely fascinated by a topic that, for the last seven years, had become increasingly present in my mind. That topic, which would soon consume my every waking thought and which I would eventually turn into a book, was sunlight.

The curiosity stemmed from an ongoing observational study of a single subject: me. I live in Vermont. Gorgeous summers, brutal winters. Over the years, I started to notice what a profound effect the different seasons had on me. Basically, winter sucked. This was not simple Seasonal Affective Disorder, a common condition in which people feel low during the winter months, and which is believed to be caused by a dearth of light entering the eyes. I didn’t feel depressed in winter. I felt as if my cells didn’t work.

After a long, cold winter and wet spring, there’s nothing like feeling the warmth of the sun on your skin. You probably know that too much sun can damage your skin and increase the risk of skin cancer. But is the sun good for you at all?

The short answer: Yes. “Sunlight is important for your health and mental well-being, but you also need to limit prolonged exposure because of the risks,” says Anna Radisic, M.D., an internal medicine physician at Hackensack Meridian Health in Lodi.

The key is finding a healthy balance. Here are five ways sunlight can boost your health, plus tips for enjoying it safely.

Summary:

Low vitamin D levels could be quietly making breast cancer surgery recovery far more painful. In a new study, patients deficient in vitamin D were three times more likely to experience moderate to severe pain after mastectomy surgery and ended up using significantly more opioid medication to cope. Researchers say vitamin D may help regulate how the body processes pain through its effects on inflammation and the immune system.

New research suggests vitamin D may support brain health and may be linked to dementia-related brain changes later in life.

A study published on April 1, 2026, in Neurology^® found that people who had higher vitamin D levels in midlife were more likely to have lower levels of tau protein in their brains years later. Tau is one of the key proteins linked to Alzheimer’s disease and other forms of dementia. When tau builds up abnormally in the brain, it can damage brain cells and interfere with memory and thinking.

The researchers followed nearly 800 adults who did not have dementia at the start of the study. Participants were about 39 years old on average when their blood vitamin D levels were first measured. More than a decade later, they had brain scans to look for signs of Alzheimer ’s-related proteins, including tau and amyloid beta.

Vitamin D deficiency is one of the most common nutritional deficiencies worldwide, yet it does not affect everyone equally. While seasonal changes, especially the winter months, play a major role in lowering vitamin D levels, there are several well-established factors that can significantly increase an individual’s risk of deficiency year-round.

Last week, we focused on the influence of the seasons on vitamin D levels, and how this time of year is when a majority of the population is at their highest risk of deficiency. Understanding the additional following risk factors for vitamin D deficiency is essential for both individuals and practitioners, as it helps identify who may need higher intake, closer monitoring, or more frequent testing year-round.

New Dr. John Campbell video reviewing the 2014 research paper reporting a statistical error in the estimation of the Recommended Dietary Allowance for Vitamin D. The corrected amount should have been 8,895 IU/day not 600 IU/day. Learn more:

Winter in Canada means cold temperatures, snowy weather and reduced daylight hours. The season also often brings an increase in common illnesses like the cold, flu and other respiratory issues that can affect our overall health. 

Maintaining a balanced diet and an active lifestyle can help boost your immune system and mood throughout winter, but even those with the best diets can be afflicted by vitamin deficiencies. As Canadians, we’re especially susceptible to lower levels of vitamin D, which is only produced when skin is exposed to sunlight.

Miranda Popen, a nutritionist who specializes in hormone health, describes Canadians as “basically running on airplane mode for half the year” due to the lower levels of sunlight we receive. 

In 1982, PubMed, a research database, indexed 740 papers with “vitamin D” in the title. In 2020, there were 5,566. Clearly, interest has increased. Today, vitamin D is studied as a system-wide regulator and an essential component of skeletal, immune, metabolic, cardiovascular, neurological, and inflammatory processes.

Even a century ago, nutritionists feared the dangers of vitamin D deficiency. Warnings were dismissed as “alternative thinking.”

Vitamin D was discovered in the early 20th century, when researchers noticed that children deprived of sunlight developed rickets, a bone-softening disease that left them bow-legged and deformed. In 1903, Niels Ryberg Finsen, a Danish physician with Icelandic roots, received a Nobel prize for pioneering the therapeutic use of concentrated light. Sanatoriums, which emphasized sunlight exposure and cod liver oil rich in D, were common treatments for tuberculosis and other infections, but Finsen’s work explained it.

New study shows that if you reduce sun exposure enough to save 1 death from skin cancer, that would cause an extra 75-135 deaths from other causes.

Severe vitamin D deficiency is associated with a higher rate of hospitalisation for respiratory tract infections such as bronchitis and pneumonia, according to a new study led by the University of Surrey. Scientists found that those with a severe deficiency (below 15 nnmol/L) were 33 per cent more likely to be admitted to hospital for treatment than those with sufficient levels of vitamin D (at least 75 nmol/L). 

In the largest study of its kind, analysing NHS data from the UK Biobank, researchers from Surrey, in collaboration with the University of Reading and University of Oxford, investigated the association between vitamin D status and the rate of hospitalisation due to respiratory tract infections. Middle and older-aged adults are at a high risk of developing respiratory tract infections, with lower respiratory tract infections (pneumonia and bronchitis) ranking amongst the top 20 leading causes of mortality globally for individuals aged 50-74 years and in the top 10 for those aged 75 years and older. 

Key Takeaways

• The Math Error: Peer-reviewed studies confirm the official Recommended Dietary Allowance (RDA) for Vitamin D is calculated incorrectly by a factor of ten.
• The Leadership: The National Academy of Medicine (NAM), led by Dr. Victor J. Dzau, has refused to correct the error since 2014.
• The Money: While the public guidelines recommend a “starvation dose,” NAM leadership earns millions in compensation and holds ties to the pharmaceutical industry.

For over a decade, a statistical error has sat at the heart of global public health.

It sounds like a conspiracy theory, but it is a published, peer-reviewed mathematical fact. In 2014, researchers proved that the official Recommended Dietary Allowance (RDA) for Vitamin D—the number used by the FDA, the CDC, and doctors worldwide—is wrong.

Not just slightly wrong. It is off by a factor of ten.

While the science is clear, the institution in charge—the National Academy of Medicine (NAM)—has remained silent. Why? To understand the inertia, you have to look at the leadership, the money, and the “standard of care” that keeps the pharmaceutical industry profitable.

To give Canadians a boost in vitamin D, Health Canada is now requiring milk and margarine producers to more than double the amount in their products. 

According to the federal health agency, one in five Canadians aren’t getting enough of the so-called “sunshine” vitamin. Experts say that’s mainly because of a lack of sunlight, which our body uses to produce vitamin D.

“The reality is we live in Canada,” said Brenda Hartman, a nutritional sciences professor at Western University in London, Ont. “We don’t make vitamin D from the sun, you know, six to eight months of the year.”