Hello Runner,
Welcome back to your weekly moment of endurance nutrition!
Happy Weekend!
How was your week?
My week was good!
My workouts are on track, and I feel like I'm performing better because of the cooler weather. I feel like I have more energy than in the summer.
Work and studies are going full steam ahead. This month, I'm going to two conferences (one on health and the other on nutrition), and I can't wait. I love staying up to date, not only for my patients, but also so I can bring you more information and news here in the newsletter.
Well, it is almost unanimous that fall and winter are amazing for training — those long, cool runs, the races that keep us motivated — but they’re also the seasons when many runners unknowingly slip into a vitamin D deficiency.
And that can quietly mess with your performance, your recovery, and even your bones.
From what I see, the current trend is to supplement magnesium (in all forms!), even though the daily requirements for this mineral can easily be met through diet.
So, I always like to emphasize the importance of vitamin D, because most people (including runners) neglect this vitamin that is so important for our health.
Let’s talk about why this little vitamin is such a big deal!
Vitamin D isn’t just about “strong bones” (though that’s already reason enough). It plays a key role in muscle function, immune support, mental health, lower oxidative stress, and — here’s the kicker — injury prevention.
It is well known that vitamin D deficiency totally affects metabolism—far beyond calcium metabolism.
Low levels have been linked to higher risks of stress fractures, muscle fatigue, depression, inflammation, high oxidative stress, muscle atrophy, and even slower recovery after hard sessions.
When it comes to running, the last thing we want is a stress fracture, right? I believe that of all the scenarios above, a fracture is the worst of them all.
Think of vitamin D as the invisible layer of protection that helps your body absorb calcium properly and keep your muscles firing efficiently.
Without enough of it, your bones take more impact than they should, and small cracks can start forming — the kind that turn into long breaks from running if ignored.
Now, here’s the problem: in fall and winter, especially in the northern hemisphere, the sun sits lower in the sky and daylight hours shrink.
Even if you head out for a morning jog, you’re often bundled up — and your skin barely gets any UVB rays. That means your body can’t make much vitamin D on its own.
This is when nutrition and/or supplementation come in to help.
Nutrition & Habits
How to Keep Your Levels Healthy
Here’s your runner’s checklist for strong bones and steady energy all winter:
Get your levels tested.
Ask your doctor for a 25(OH)D blood test — it’s simple and tells you exactly where you stand. Ideally, you want your levels between 40–60 ng/mL (some athletes even feel best a bit higher).Consider supplementation (if needed).
Most adults do well with 1,000–2,000 IU/day during fall and winter, but your exact dose should depend on your blood test.
Important: don’t self-prescribe mega doses. More isn’t better — balance is key.
→ Vitamin D overdose can lead to vitamin D toxicity.
Clinical manifestations of vitamin D toxicity may include hypercalcemia (excess calcium in the blood), nausea, vomiting, muscle weakness, polyuria (excessive or an abnormally large production of urine), nephrocalcinosis (too much calcium deposited in the kidneys), and renal failure.
Eat foods that give you a boost.
Fatty fish like wild-caught salmon, mackerel, halibut, and sardines.
Canned light tuna.
Egg yolks (yes, don’t skip them).
Fortified dairy or plant milks.
Mushrooms that are exposed to sunlight.
Pair with healthy fats.
Vitamin D is fat-soluble — meaning it absorbs better when eaten with a little fat. So drizzle some olive oil on your veggies or pair your eggs with avocado toast.Get some light when you can.
Aim for midday exposure between 10 a.m. and 3 p.m., when UVB rays are most direct and effective for vitamin D synthesis. Expose as much skin as possible, such as arms, legs, and face, without sunscreen. Fifteen to thirty minutes can make a difference — plus, it just feels good.
In countries where winters are harsh and you cannot go outside with parts of your body exposed, the best way to replenish vitamin D deficiency is through supplementation.
As the days get shorter and your kms build up — take a moment to check in with your vitamin D.
It’s one of those quiet details that separates just getting through winter from thriving through it.
This week’s challenge: Book a quick vitamin D blood test and look at your diet for a few of those “sunshine foods.” Your metabolism and future bones will thank you.
Track of the week 🎧️
This week's Track of the Week it's a remix of an old song that I recently discovered (yet another one, I've been discovering some gems lately), and I love the beat. Perfect for a Zone 3 run.
I've chosen the track Give It To Me by Lucas Estrada, Daytona
Any questions or something you would like to share, drop me an email
Wishing you a great weekend and week ahead!
Here’s to health and good runs⚡️
Ana Paula Alonso