When Dr. Bernadette Atanga relocated from the sun-soaked streets of Houston, Texas, to the often overcast skies of Michigan for her medical training, she soon noticed a change in her well-being.

As a physician specializing in internal medicine and pediatrics, Dr. Atanga found herself suddenly deprived of the regular sunlight she had always enjoyed. Over the four years of her residency, she began to attribute her increasing tiredness to the rigors of her demanding job.

“As a busy physician and mom, my growing fatigue initially felt like burnout until persistent dizziness developed,” she shared with the Daily Mail.

Seeking answers, Dr. Atanga visited her primary care physician, who conducted various tests. Most results appeared normal, except for one crucial finding: her vitamin D levels were significantly below the recommended levels for adults, nearly half of what U.S. health officials suggest.

Vitamin D is a vital nutrient synthesized by the body when the skin is exposed to sunlight. It is also present in certain foods, such as fatty fish like salmon and mackerel, egg yolks, and fortified products like milk, yogurt, and orange juice.

This nutrient plays a critical role in helping the gut absorb calcium and phosphorus, essential for maintaining strong bones. A deficiency in vitamin D can deprive cells and muscles of energy, causing fatigue, pain, and weakness.

‘After several weeks of high-dose supplementation prescribed by my endocrinologist, both the fatigue and dizziness resolved,’ Atanga said.

Atanga was one of nearly two-thirds of Americans who are low or deficient in vitamin D – she joined the likes of actor and wellness guru Gwyneth Paltrow, who revealed in 2010 that she was severely lacking the essential nutrient.

Vitamin D is essential for maintaining bone health, improving immune responses and protecting against brain degeneration, but most Americans don’t get enough

Physicians and dietitians speaking with the Daily Mail revealed the vitamin’s benefits go beyond bone and muscle health. Emerging research shows it may boost hair growth, protect the immune system and improve mental health, too.

‘Vitamin D is one of the most talked-about nutrients in medicine, but people still don’t understand it,’ Dr Daniel Ghiyam, medical director and longevity expert at MedPodLA, told the Daily Mail. 

‘I see it more as a hormone that affects multiple systems in the body – such as bone metabolism, immunity, neuromuscular function, and mood and cognition – than as a straight vitamin.’

While most doctors recommend upping vitamin D intake primarily from foods, supplements are also widespread. A month’s supply, depending on the brand and dosage, typically costs between $4 and $25. This means the cost per pill could be as low as 13 cents.

‘Most people struggle to get enough from diet alone,’ Dr Raj Dasgupta, internal medicine physician and chief medical advisor for Sleepopolis, told the Daily Mail. ‘For most adults, 600 to 800 international units (IU) per day is the recommended amount, although many people need closer to 1,000 to 2,000 IU to maintain healthy levels.’

Over-the-counter vitamin D pills usually range in dosage from 400 to 10,000 IU, but those available via prescription for severe deficiencies offer up to 50,000 IU.

While the effects of vitamin D on bone and muscle health are well known, recent studies have pointed toward a more unexpected benefit: hair growth.

‘Vitamin D helps to support the hair cycle and the hair follicle itself. With a deficiency, it can halt the growth phase and prematurely place the follicle into the resting phase, which will ultimately cause that hair to shed out,’ Dr Christina Han, dermatologist and medical director at XYON Health, told the Daily Mail. 

She noted hair loss from vitamin D deficiency is especially common in post-menopausal women due to the natural loss of estrogen. Low estrogen levels have been shown to shrink hair follicles, leaving women in this age range who are vitamin D deficient particularly prone to developing bald spots.

Han also points to the skin benefits that can come from vitamin D.

Vitamin D is an antioxidant, a compound that protects the body’s cells from damage caused by unstable molecules. These have been shown to reduce inflammation and boost immune health.

‘UV and sun-induced damage to the skin creates oxidative stress and can be cell damaging,’ Han said. ‘Vitamin D helps to repair damage and reduce oxidative byproducts in the skin… [and] keep the skin turnover normal and the skin barrier protected against infection and overall immunity.’

Gwyneth Paltrow (pictured in January) has previously been open about having a vitamin D deficiency and taking supplements

Vitamin D is strongly linked to sun exposure, but people with darker skin or who live in colder environments may be at a greater risk of deficiency

People with darker skin are also at a greater risk of vitamin D deficiency because they have higher amounts of melanin. Melanin, a natural pigment, can act as a barrier against the UV radiation needed for the body to create vitamin D.

Han noted that in her Vancouver-based practice, she sees many patients that have a deficiency due to lack of sun exposure.

‘It can affect all people, but I commonly see it in women who come in for hair loss, young and old,’ she said. 

Vitamin D also has links to mental health, Dr Wesley Buckle, a licensed naturopathic doctor at The Oasis Addiction Treatment Center in California, told the Daily Mail.

‘Low levels of vitamin D is associated with seasonal mood changes and higher rates of depression,’ he said. 

He explained that this is because the brain has multiple vitamin D receptors, particularly in areas responsible for cognition, mood and memory. So having a deficiency raises the risks of conditions such as depression and anxiety.

As for brain health, science also suggests having a vitamin D deficiency increases the risk of developing dementia. Low levels have been linked to increased inflammation and neurodegeneration in the brain, which reduces the brain’s ability to clear out toxic proteins like amyloid-beta that have been shown to cause Alzheimer’s disease, the most common form of dementia. 

Research from the University of South Australia found that getting an adequate level of vitamin D could prevent up to 17 percent of dementia cases.  

Scientist Dr David Jan, head of research and development and manufacturing at Aonic, told the Daily Mail that the ‘most reliable way to know your vitamin D status is with a blood test, rather than guessing based on symptoms alone.’

Overdosing is possible, he said.

‘Because vitamin D is stored in the body, taking too much can cause calcium levels to rise, which may affect the kidneys or heart,’ Jan explained to the Daily Mail. ‘People with kidney disease, a history of kidney stones or high calcium levels should talk with a doctor before supplementing.’

He also recommended opting for a vitamin D3 supplement instead of vitamin D2, as it is generally absorbed more effectively. However, D3 is derived from animal sources such as sheep lanolin and fish, so D2 remains an option for vegetarians and vegans.

Dasgupta also urged folks to speak with a physician before starting any new supplement.

‘The goal is fixing your deficiency safely,’ he said, ‘not mega-dosing and causing other issues.’