At 75 years old, living with Parkinson’s Disease, I have become increasingly interested in therapies that support strength, mobility, cognition, immunity, and long-term resilience. One of the supplements I take consistently is Vitamin D3. Although many people think of Vitamin D simply as a “bone vitamin,” the reality is that it functions more like a hormone and affects nearly every system in the body. For me, Vitamin D3 represents an important part of maintaining quality of life as I age and manage a chronic neurologic condition.

One of the primary reasons I take Vitamin D3 is bone and muscle protection. As we age, the risks of osteoporosis, muscle weakness, and falls rise dramatically. In Parkinson’s Disease, balance and gait instability can already increase fall risk, so preserving muscle function and bone density becomes especially important. Vitamin D helps the body absorb calcium and maintain skeletal strength, but it also appears to improve muscle performance and neuromuscular coordination. Low Vitamin D levels have been associated with muscle weakness, slower walking speed, and increased falls in older adults. In someone with Parkinson’s, where mobility is already challenged, that becomes highly relevant.

I also take Vitamin D3 because of its potential role in brain health and neuroprotection. Researchers have found Vitamin D receptors throughout the brain, including in areas involved in movement and cognition. Some observational studies have shown that low Vitamin D levels are more common in people with Parkinson’s Disease and may correlate with worse symptoms or faster progression. While Vitamin D is not a treatment or cure for Parkinson’s, there is scientific interest in whether maintaining adequate levels might help support neuronal health, reduce inflammation, and improve overall neurologic function. At the very least, avoiding deficiency seems prudent in a disease that already places stress on the nervous system.

Inflammation control is another reason I take Vitamin D3. Chronic inflammation is increasingly recognized as a contributor to aging and degenerative disease. Vitamin D helps regulate immune signaling and may reduce excessive inflammatory responses. This is important not only for neurologic conditions but for overall cardiovascular and metabolic health as well. In many ways, healthy aging depends on maintaining balance in the immune system—strong enough to defend against infection, but not chronically overactivated. Vitamin D appears to help modulate that balance.

I also pay attention to Vitamin D because hormone therapies can interact with bone and metabolic health. I take thyroid hormone in the form of T3 and weekly testosterone replacement. Testosterone can support muscle mass, energy, mood, and bone density, but these benefits are optimized when the body also has adequate Vitamin D. There is evidence that Vitamin D status may influence testosterone function and musculoskeletal performance. Similarly, thyroid hormone affects bone turnover. Excess thyroid hormone can accelerate bone loss over time if dosing is too high. Because of that, maintaining sufficient Vitamin D becomes part of a broader strategy to protect bone integrity while using hormone therapies thoughtfully.

Another important reason I take Vitamin D3 is immune support. Older adults are more vulnerable to infections, and Vitamin D appears to play a role in both innate and adaptive

immunity. Studies have associated low Vitamin D levels with increased susceptibility to respiratory infections and poorer immune resilience. While Vitamin D is not a substitute for good medical care or healthy habits, maintaining adequate levels may help the immune system function more effectively.

Mood and cognition are also part of the equation. Parkinson’s Disease can affect more than movement; it may also impact mood, motivation, sleep, and cognitive sharpness. Some research has linked low Vitamin D levels with depression, fatigue, and cognitive decline in older adults. The evidence is not definitive, but many clinicians feel that maintaining healthy Vitamin D levels is a reasonable component of supporting emotional and cognitive well-being, particularly in aging populations.

Importantly, I take Vitamin D3 (Vitamin D2 is less active) with monitoring rather than blindly. More is not always better. Blood testing for 25-hydroxy Vitamin D can help guide dosing and prevent excessive levels, which can lead to complications such as elevated calcium. Because I live in a northern climate, I have relatively little exposure to sunlight, and therefore, little Vitamin D through most of the year. This is why I feel that the recommendations of Vitamin D (usually 1000 or 2000 iu daily) are inadequate. I take 5000 iu daily. And I sometimes double it for a few days if it’s a particularly dark winter, I’m indoors a lot, or I’m on the verge of getting a cold. Mostly, I’m guided by the lab testing.

For me, Vitamin D3 is not a miracle cure. It is part of a broader philosophy of aging proactively rather than passively. Parkinson’s Disease may limit certain aspects of life, but I still want to preserve strength, independence, cognition, immunity, and resilience for as long as possible.

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