The short answer
Southern California has enough sunshine to make vitamin D year-round. The problem is that many men are not in it. Long days indoors, darker skin, extra body fat and sensible sunscreen habits all cut into what the sun can do, so a man in Los Angeles can be low in vitamin D while living in one of the sunniest cities in the country.
The fix is not guesswork. Ordinary daily amounts are safe without testing, but if you are thinking about high-dose supplements, or have a reason to suspect a real deficiency, a blood level should guide the decision.
The sun is not the problem in Los Angeles
The latitude works in your favor. A classic 1988 study exposed vitamin D’s precursor in skin samples to sunlight in different cities. In Boston, at 42 degrees north, winter sun from November through February produced no previtamin D at all, and in Edmonton the “vitamin D winter” ran from October through March. Further south, at 34 degrees north, which is the latitude of Los Angeles, sunlight still made previtamin D in the middle of winter.
So the light is available in January. What changes the picture for most men is how little of it reaches their skin.
Indoor work: the biggest factor most men control
Working indoors is strongly linked to lower vitamin D. A 2017 systematic review of 71 studies across many occupations found that indoor workers averaged a 25-hydroxyvitamin D level of 40.6 nmol/L against 66.7 nmol/L for outdoor workers. Deficiency, defined in that review as below 50 nmol/L (20 ng/mL), affected 78% of indoor workers and 80% of shift workers, against 48% of outdoor workers.
Think about a typical week for many men in the region: a commute in a car, a day in an office, warehouse or hospital, a gym session indoors, and dinner after sunset. A bright desk by the window is not the same as time outdoors with sun on bare skin. Our page for night shift workers covers a group that misses daylight almost entirely.
Skin tone and body fat change the math
Two biological factors make the same sunlight less effective.
Darker skin. Melanin protects against UV damage, and it also slows vitamin D production. In national survey data from 2005 to 2006, a 2011 analysis found vitamin D deficiency, defined as 20 ng/mL or lower, in 41.6% of U.S. adults overall, 82.1% of Black adults and 69.2% of Hispanic adults. Being non-white, obese, not college educated and not drinking milk daily were each independently linked to deficiency. In a region as diverse as Los Angeles County, that matters. Our page for men with darker skin tones covers other ways skin type shapes care.
Higher body fat. Vitamin D is fat-soluble, and fat tissue holds onto it. In a 2000 study, men and women with obesity had lower baseline vitamin D, and after the same whole-body UV exposure, the rise in blood vitamin D3 was 57% lower than in lean people. Their skin made vitamin D normally; less of it reached the bloodstream. A man carrying extra weight may need more vitamin D to reach the same level, which is one reason a test is useful before guessing at a dose.
What about sunscreen?
Sunscreen is often blamed, and the evidence says the effect is smaller than people fear. In a 2019 study of volunteers on a sunny holiday with a very high UV index, people who applied SPF 15 sunscreen properly were protected from sunburn, yet their vitamin D levels still rose significantly over the week.
Southern California sun also causes sun spots, wrinkles and skin cancer, so keeping sunscreen on your face and neck is still the right call. The vitamin D you need can come from a short time outdoors on arms and legs, from food, or from a supplement.
Small changes that add up
You do not need to lie on the beach to make a difference. For men who work indoors, the most practical shifts are small and regular:
- Take a short walk outside at midday instead of eating at your desk
- Hold a walking meeting or phone call outdoors when you can
- Move one weekly workout outside, such as a hike, run or ride
- Keep sunscreen on your face and neck, and let arms and legs get brief exposure
- Never aim for a tan or a burn; short, regular time outside is the goal
These habits help mood, fitness and sleep as well as vitamin D, and they cost nothing. They also make any lab result easier to interpret, because your provider can see what your level looks like with a realistic routine rather than an occasional sunny weekend.
Why a blood level beats guesswork
Here is the nuance. The Endocrine Society’s 2024 guideline suggests against routine vitamin D screening in healthy adults, including adults with dark complexion or obesity, and points healthy adults under 50 to the standard intake of 600 IU a day. Taking that ordinary amount does not require a test.
Guesswork becomes a problem at the other end. Men often start 5,000 IU or more a day on the advice of a podcast, or stop and start for years, without knowing whether they were low to begin with. Very high doses taken for long periods can cause harm, which is uncommon but avoidable, while a true deficiency leaves bones short of what they need. A blood test makes sense when:
- You are considering a dose well above the standard daily amount
- You have bone loss, a low-trauma fracture or a condition that affects absorption, such as celiac or Crohn disease
- You have several risk factors at once, such as indoor work, darker skin and a high body fat percentage
- You have been supplementing for a long time at a dose you chose yourself
Our page on the vitamin D blood test explains the 20 and 30 ng/mL cutoffs, and the one on vitamin D3 for men with low levels covers how low levels are treated. If bones are the worry, see low bone density in men.
How Ultimate Male checks vitamin D
Vitamin D is part of our targeted preventative panel, alongside ApoB, Lp(a), hs-CRP, iron, zinc, B12 and liver and kidney markers, and the nutrient deficiency panel page explains the nutrient side. Through our preventative blood testing, blood is drawn on site at San Gabriel or Downey and results come back in 24 to 48 hours.
A PA-C or MD reads your level against your work schedule, skin type, weight and any supplements you already take, then explains whether to change anything and by how much. If you have been guessing for years, the free 10-minute phone call at 626-319-5261 is a simple place to start.
