Points Capital

By early November, a lot of us in the northern US hit the same wall: you leave for work in the dark, sit under office lights all day, and come home in the dark again. Then you burn a stash of points on a week in Puerto Rico, Cancún or Maui, and you come back feeling like a different person. Part of that is just vacation. But winter also changes how much vitamin D your skin can make, and frequent travelers who spend their “outdoor” time in airports, planes and hotel gyms may get less sun than they think.

So this week we looked at what Dr. Rhonda Patrick of FoundMyFitness has said about why vitamin D levels so often stay low, and what that means for anyone planning a winter sun trip on points.

What Dr. Rhonda Patrick says about low vitamin D

In a FoundMyFitness clip titled “Why Vitamin D Levels Stay Low” (taken from her appearance on The Tim Ferriss Show), Dr. Patrick walks through several reasons someone can take vitamin D or get sun and still test low. Her main points, in our own words:

• People respond very differently. She points to common genetic variants that may affect how much vitamin D a person makes from sun or gets from supplements. Her bottom line is blunt: “This is something you have to measure because, as you mentioned, there is huge variation.”
• Skin pigment matters. “Melanin, the darker skin pigment, is a natural sunscreen,” she says, so people with darker skin need considerably more sun exposure to make the same amount of vitamin D. Sunscreen also reduces production.
• Magnesium plays a role. She explains that the conversion to the form doctors measure in a blood test, 25-hydroxyvitamin D, depends on magnesium, and she cites US survey data linking low magnesium intake with lower vitamin D levels.
• Labels are not always accurate. She notes some supplements have been found to contain much less vitamin D than the label claims.

Dr. Patrick also says she personally aims for a higher blood level than many official guidelines treat as adequate, and she argues that the right intake should be worked out person by person, with retesting, rather than from a one-size-fits-all number. That is her view. The NIH Office of Dietary Supplements notes that the Food and Nutrition Board considers a blood level of 20 ng/mL or more sufficient for most people, and experts still disagree about the ideal range. That is exactly the kind of question to take to your own doctor.

Why travel and winter make this trickier

According to the NIH’s health professional fact sheet, season, time of day, length of day, cloud cover, smog, skin pigment and sunscreen all affect how much vitamin D your skin makes from UVB light. A few of those line up uncomfortably well with a road warrior’s life:

• That sunny window seat does not count. The NIH is clear that UVB does not penetrate glass, so sun through a plane, hotel or lounge window does not produce vitamin D.
• Smog cuts it too. The NIH consumer fact sheet lists smog among the factors that reduce vitamin D production, one more strike against hazy big-city stopovers.
• Short winter days, long indoor days. Business trips in winter often mean dark mornings, conference rooms and evening flights, with little skin exposed to midday sun.
• Latitude. The NIH notes that people who live near the equator get more sun exposure and have higher vitamin D levels, which is one reason a December trip south feels so different from a December at home.

The Points Capital winter sun playbook

Before the trip

1. Ask your doctor about a test. If you are curious where you stand, a 25-hydroxyvitamin D blood test is how it is measured. Dr. Patrick’s whole point is that guessing does not work well because people vary so much.
2. Do not self-prescribe big doses. If you already take vitamin D or are thinking about it, talk to your doctor or pharmacist first. The NIH notes vitamin D can interact with some medications, and that upper limits count intake from food, drinks and supplements combined.
3. Book for daylight. When you are choosing award flights, a morning departure that lands you at a sunny destination by early afternoon gives you a usable first day outside instead of an evening arrival.

During the trip

4. Get outside, not just near a window. Swap the hotel treadmill for a walk on the beach path or a morning swim. Fresh air and daylight are worth more than a view through glass.
5. Keep sun safety in the plan. The NIH says sunscreen limits vitamin D production but still recommends SPF 15 or higher when you are outdoors, and it notes your skin limits how much vitamin D it makes from sunshine anyway. More sun is not better past a point: avoid burning, use shade and cover up during long exposures.
6. Eat for it. The NIH lists fatty fish as among the best natural food sources, with smaller amounts in egg yolks, beef liver, cheese and some mushrooms, and notes that fortified milks, including many plant-based milks, supply much of the vitamin D in the US diet. Grilled fish by the water is an easy win on a beach trip.

After you get home

7. Do not treat one week as a winter fix. A sunny long weekend is great for your mood and your step count, but it is not a plan for the next three months of short days.
8. Keep the outdoor habit. Even at home, a midday walk outside on clear days beats another lap of the office, and it gets you daylight and fresh air either way.
9. Follow up if you tested. If your doctor suggested changes, Dr. Patrick’s approach of retesting rather than guessing is a sensible one to raise at your next visit.

Our take

Sunshine and fresh air are already near the top of the Points Capital team’s health priorities, so a winter sun redemption is an easy sell for us. What Dr. Patrick’s clip adds is a useful reality check: vitamin D is personal, and the only way to know your number is to measure it. For frequent travelers, the bigger lesson is that hours spent next to airport and airplane windows do not count. Use your points to get somewhere warm, then actually go outside, protect your skin, eat well, and leave the dosing questions to you and your doctor.

Sources

• FoundMyFitness, “Why Vitamin D Levels Stay Low” (Dr. Rhonda Patrick)
• FoundMyFitness, Vitamin D articles, videos and studies
• NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Health Professionals
• NIH Office of Dietary Supplements, Vitamin D Fact Sheet for Consumers

This article is for general information only and is not medical advice. Talk to your doctor before changing your diet, exercise, sleep or supplement routine.