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Today’s Health Upgrade

• Sunscreen does what to your Vitamin D?

• Puppy chow (what your dog deserves)

• An inside look at ketone shots

• Why it’s harder to make friends as you age

Health 
Can Sunscreen Lower Vitamin D?

There’s a recent push against using sunscreen. One reason people say to avoid it is that it reduces Vitamin D production. 

Many of you asked us to investigate, and what we found is a hint of truth with a lot of misleading spin. 

Research suggests sunscreen can reduce vitamin D production, but that’s also a sign it’s working.

The real question isn’t whether sunscreen affects vitamin D. It’s whether the effect is large enough to create a problem.

In one study, researchers randomly assigned adults to apply SPF 50+ every day or continue their usual sunscreen habits. Vitamin D levels in the daily-use group barely changed, while levels in the control group increased. 

But this makes sense: Your skin makes vitamin D when it interacts with UVB rays, and sunscreen’s job is to block those same rays before they damage your skin.

So this isn’t as much of a problem as a sign that sunscreen is blocking the sun's damage, and therefore reducing vitamin D production at the same time. 

And if you’re using sunscreen to prevent skin damage or reduce cancer risk, sunscreen protects against the disease, which is a much bigger threat to your health

Swapping a little more Vitamin D for a higher risk of skin cancer is not a good trade. 

If you’re worried about your Vitamin D levels, we recommend having them tested. Unless you’re deficient, getting more Vitamin D doesn’t appear to do much to improve your health. 

If you need more, you can close the gap with fatty fish like salmon or trout, cod liver oil, UV-exposed mushrooms, or Vitamin D-fortified milk. Or, you can also take a high-quality Vitamin D supplement.

Together With Sundays With Dogs 
Your Dog (Like Your Body) Deserves The Best

Arnold’s love for animals is no secret. From dogs and horses to a pig named Schnelly Schwarzenegger, his home is full of beloved companions. 

And just like with his own diet, Arnold believes animals deserve the best food to fuel their health, though he’s been known to sneak his pets an oatmeal cookie or two.

That’s why we tested different dog foods for animal lovers. After all, your pup deserves food as good as yours. 

Sundays for Dogs offers the perfect combination of health and convenience. Other dog foods force you to choose. Cheap kibble? Easy, but it’s full of fillers and lacks nutrients. Fresh meals? Nutritious, but it means freezing, thawing, and cooking. Sundays does it all, with air-dried, human-grade ingredients that are shelf-stable and ready to pour.

Superior Nutrition: Sundays beats traditional kibble 39-0 in a third-party taste test, featuring recipes with short lists of meats, fruits, and veggies you’d recognize.

Easy to Serve: No fridge, no prep, no cleanup. Just scoop it into a bowl and watch your dog devour it.

Better Ingredients: Air-dried low and slow in the USA, Sundays retains maximum nutrition while delivering jerky-style pieces your dog will love.

Sundays is all about raising the bar for your best friend’s diet. This isn’t just dog food; it’s human-grade nutrition made simple.

Try the Sundays Challenge: Let your dog decide. Put Sundays next to your current food, and see which one wins. Use code PUMPCLUB for 50% off your first order and see what your dog does with it.

Your Money Is No Good Here
The Ketone Shot That Promises More Than It Delivers

Energy in the bottle, none of the caffeine

That’s the promise of exogenous ketones. You take a shot, flood your body with ketones, and unlock sharper focus, better endurance, and fewer cravings.

It sounds great on paper, and when a brand came to us to partner, we did what we do with sponsors: we got the product, tested it with our community, and dug into the research. 

As many brands have learned, sometimes asking for a partnership can lead to the wrong kind of attention. 

When you look at the research, the bottle delivers ketones in a way that shows in your blood. But that’s not what matters most. 

Scientists examined whether exogenous ketones improve performance or cognition, but the supplement showed little to no effect.

That’s because changing a biomarker is not the same as changing an outcome.

When researchers reviewed randomized trials focused on endurance, exogenous ketones did not meaningfully improve time-trial performance, time to exhaustion, VO₂ max, or even how hard the exercise felt. 

But it’s not just exercise. Ketone products suggest that the shot will improve focus. Your brain can use ketones for energy, which could benefit older adults and people whose brains may have more difficulty using glucose efficiently.

But the studies where you drink ketones (instead of following a diet that puts you in ketosis) don’t offer any strong evidence that you’ll experience a boost in focus, at least not from the shots. 

A recent meta-analysis suggested there might be a small cognitive effect, but it wasn’t due to the bottled-up ketones. That came from MCT-based precursors, which is something entirely different from the ketone shots. 

And another recent study even found that a ketone drink reduced blood flow to the brain, another reminder that “more brain fuel” is a much cleaner marketing story than biological reality.

One study found that a ketone drink temporarily lowered ghrelin, a hormone involved in hunger. But it appears the results were driven by the use of a more potent ketone ester, which produced roughly twice the blood ketone levels achieved with typical shots.

If you want to drink ketones or find that they help you, then your results should determine what works best for you. No study can control what works in every scenario for every person. 

But if you’re curious, the research (at this point) suggests that buying ketone shots won’t buy you more stamina, sharper thinking, or better control over your cravings.

We passed on the product and the partnership, and suggest your time and money are better spent elsewhere, too. 

Social Health 
The Real Reason Making Friends Gets Harder

Loneliness might be one of the most underrated variables of overall health. 

Studies suggest that people who are socially connected appear to be happier, healthier, and live longer. 

And yet, we all know the reality. At some point, we don’t see our old friends as much. And it feels harder to make new friends. 

Life and adulthood throw in the never-ending mix of surprises, obligations, and exhaustion. 

Were you better at making friends when you were younger? The research offers a perspective that might help you recapture some social magic.

Making friends doesn’t necessarily get harder because you get worse at it. The structure that made friendship easier disappeared.

When you’re younger, school, sports, dorms, and early jobs create repeated contact without requiring much effort. Adulthood replaces that built-in time with work, kids, errands, and calendars that rarely line up.

Research suggests closeness often grows through repetition, not instant chemistry. One study found that spending more time together was associated with stronger friendships. 

The researchers estimated it took roughly 40 to 60 hours to move beyond an acquaintance, about 80 to 100 hours to become friends, and more than 200 hours to become close.

You don’t need to start logging hours like a time sheet at work because those aren’t precise requirements, but the larger point matters: friendship needs time in the same place, often without every interaction being carefully planned.

And then there’s the other side that slows connection: your brain can make rebuilding that structure feel riskier than it is.

Across 13 experiments, people consistently underestimate how much someone would appreciate hearing from them. The effect was even stronger when the message was unexpected, or the relationship had become more distant. And another study found that after conversations, people tend to underestimate how much the other person liked them.

It’s a recipe for loneliness: you have less time with people, and you’re less likely to reach out because you don’t realize how much your messages mean to people when they are received. 

This doesn’t prove that sending one text will cure loneliness. But it does suggest holding back and not reaching out contributes to the lack of connectedness. 

As Arnold says, it’s “reps, reps, reps,” and your friendships are no different. 

If you want to feel more connected, schedule time for text, talk, or meet in person. You don’t need to be around people all the time, but you do need to maintain the relationship.

And if you’re looking to make new friends, pick one activity that meets at the same time and place each week. It’s a chance to meet people with similar interests, routinely. Or you could take someone you recently met and invite them to join something you already do. 

Friendship rarely disappears because nobody cares. More often than not, life removes repetition, and you just need to commit to rebuilding it.

The Positive Corner of The Internet
About Arnold’s Pump Club Editorial Standards

We do things a bit differently here, starting with transparency.

1. The Content: All APC emails are researched, written, and fact-checked by the APC editors (see bottom of the email), with written contributions from Arnold (noted with “Arnold’s Corner”). Links take you to original studies (not second-hand sources).

2. Does AI play a role? Not for the primary content, but it is used in two ways. The main items are original content written by the APC team. The summaries at the end are AI-generated based on the human-written content above. We also use an AI tool to edit and review our interpretations of the research, ensuring scientific accuracy. We don’t assume AI is right, but we use technology to hold ourselves accountable.

3. Yes, we have partners (all clearly noted by “Together With”). Why? Because it allows us to keep the APC emails free. We first test products, and then reach out to potential partners who offer ways to help you improve every day. The bar is set high, and to date, we have turned down millions in ad deals. (Example: we will not partner with any non-certified supplements or those without evidence in human trials). If we won’t buy the product, we won’t recommend it to you. And if there’s no evidence it works, then there’s no place for it here.

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Publisher: Arnold Schwarzenegger​

Editors-in-chief: Adam Bornstein and Daniel Ketchell