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Vitamin D—Vital for Maintaining Muscle Strength


The day before his 88th birthday, Clint Eastwood was asked how me remained so young and active. Eastwood’s reply: “I don't let the old man in.” Love that!

While we can’t halt aging altogether, we may be able to slow the process down—not “letting the old man in” for a while (“old woman” as well, of course)—via several areas, including diet, supplementation, exercise, getting sufficient sleep, and many others far too numerous to list here.

One area in delaying the aging process that’s of importance, especially for athletes, is maintaining muscle strength, the loss of which is formally known as dynapenia. The National Center for Biotechnology Information elaborates:

Dynapenia (pronounced dahy-nuh-pē-nē-a, Greek translation for poverty of strength, power, or force) is the age-associated loss of muscle strength that is not caused by neurologic or muscular diseases. Dynapenia predisposes older adults to an increased risk for functional limitations and mortality. [1]

A study detailed in the peer-reviewed journal Calcified Tissue International and Musculoskeletal Research [2] found a connection between lower levels of vitamin D and a greater risk of developing dynapenia. Data from over 3,200 men and women. Ages 50 and higher, was utilized for this study. None of the participants showed signs of dynapenia as determined by grip strength at the onset of the study. The participants’ serum 25-hydroxyvitamin D levels were also measured at that time, and were categorized as sufficient, insufficient, or deficient. The researchers reassessed participants’ grip strength after a four-year period.

Sufficient – 25-hydroxyvitamin D levels of at least 20 ng/mL
Insufficient – 25-hydroxyvitamin D levels of 12-20 ng/mL
Deficient - 25-hydroxyvitamin D levels of less than 12 ng/mL

IMPORTANT NOTE: Optimal range is between 50–80 ng/mL

The results showed that, compared to the Sufficient group, the Insufficient group had a significant 55% greater risk of developing dynapenia, while the Deficient group had a massive 70% greater risk.

One of the lead researchers, Dr. Tiago da Silva Alexandre, states “Vitamin D is known to participate in various functions of the organism. It’s a hormone and its many roles include helping to repair muscles and releasing calcium for muscle contraction kinetics. It was therefore expected to cause muscle alterations of some kind. That’s exactly what our study proved.” He continued, “Another conclusion to be derived from the results of the study is that it’s important to take vitamin D if you have a deficiency or insufficiency. It’s necessary to explain to people that they risk losing muscle strength if they don’t get enough vitamin D.”

One thing that should catch your eye is that the “sufficient” category started at a level (20 ng/mL) that’s far below the optimal level of 50–80 ng/mL. We don’t know how many of the participants were near or within the optimal level, but just think about how higher the risk of dynapenia would be if the “sufficient” group were not close to or inside the ideal 50-80 ng/mL level.


Vitamin D is arguably the most researched nutrient of all, and the benefits that optimal levels supply are numerous and wide-ranging. These benefits also include helping us maintain muscle strength as we get older, which is vitally important for everyone, not just athletes.

The best way to know how much vitamin D you need is via a 25-hydroxyvitamin D blood test, also called a 25(OH) D test. For many people, an amount of 2,000 IU (50 mcg) is oftentimes completely sufficient, and for others who may need more, it is an excellent starting point. 2,000 IU (50 mcg) is the amount found in one softgel capsule of EnDuro D. In addition, EnDuro D contains an ideal amount of vitamin K2, which provides its own powerful benefits, while complementing vitamin D perfectly.


1 comment

I had been taking 10,000 D (a supposedly quality D sold at my physician’s pharmacy with his name on it) for years without ever reaching optimal levels, until I started taking Hammer’s Enduro D. I do supplement with plain D, as 2,000 is not quite enough for me, but with optimal results. This product gives results. I would recommend it, but I don’t want Hammer to run out of inventory!

Carol Carter

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