Researchers in Armenia tested three different ways to give vitamin D supplements to people who didn’t have enough of it. Some people took small doses every day, others took medium doses once a week, and a third group took large doses every other week. After 12 weeks, all three groups had healthy vitamin D levels in their blood. This means doctors can choose whichever method works best for each patient based on their preferences and lifestyle, since they all work equally well.

The Quick Take

  • What they studied: Whether three different schedules for taking vitamin D supplements work equally well to bring vitamin D levels back to normal
  • Who participated: 60 adults living in Yerevan, Armenia (average age 45, mostly women) who all had low vitamin D levels at the start
  • Key finding: All three dosing schedules successfully raised vitamin D levels to healthy ranges within 12 weeks. By week 36, all groups had similar vitamin D levels, though one group ended slightly higher than another
  • What it means for you: If your doctor says you need vitamin D supplements, you have flexibility in how you take them. You can choose daily pills, weekly doses, or every-other-week doses based on what fits your life best—they all work

The Research Details

This was a randomized controlled trial, which is one of the strongest types of research studies. Researchers recruited 60 adults in Armenia who had low vitamin D levels and randomly assigned them to one of three groups. Each group received a different vitamin D dosing schedule: Group A took 7,000 IU (international units) every single day for 12 weeks, then 3,500 IU daily for the next 24 weeks. Group B took 50,000 IU once per week for 12 weeks, then 25,000 IU weekly for 24 weeks. Group C took 100,000 IU every other week for 12 weeks, then 50,000 IU every other week for 24 weeks. The researchers measured everyone’s vitamin D blood levels at the beginning and then at weeks 4, 8, 12, 24, and 36 to track how quickly their levels improved.

The study was well-designed because it compared three different approaches head-to-head in the same population. By randomly assigning people to groups, the researchers reduced the chance that differences between people would affect the results. All participants were from the same city and had similar starting vitamin D levels, which makes the comparison fair.

This research matters because vitamin D deficiency is a common health problem worldwide, but doctors don’t always agree on the best way to fix it. Different countries have different guidelines, and Armenia hadn’t tested which approach works best for their population. By comparing three realistic dosing schedules, this study helps doctors understand that they don’t need to stick to just one method—they can personalize treatment based on what works for each patient

This study has several strengths: it used random assignment to groups, measured vitamin D levels multiple times over 36 weeks, and included a reasonable sample size of 60 people. However, the study was relatively small and only included people from one city in Armenia, so results might differ in other populations. The study also didn’t track whether people actually took their supplements as prescribed, which could affect the results. Additionally, 80% of participants were women, so the findings may not apply equally to men

What the Results Show

All three groups showed rapid improvements in vitamin D levels during the first 8 weeks. From the starting point to week 4, everyone’s vitamin D levels jumped significantly. From week 4 to week 8, levels continued to rise. After week 8, the increases slowed down and leveled off, with most people reaching vitamin D levels in the mid-40s range (measured in ng/mL, which is how doctors measure vitamin D).

When comparing the three groups directly, there were very few meaningful differences. At the start, Group A (daily dosing) had slightly higher vitamin D levels than Group B (weekly dosing)—21.0 versus 16.9 ng/mL. This small difference continued through the study, with Group A ending at 47.7 ng/mL and Group B at 40.2 ng/mL at week 36. However, both of these levels are considered healthy and sufficient. Group C (every-other-week dosing) fell in between the other two groups.

The key takeaway is that by week 12, all three groups had reached healthy vitamin D levels, and these levels stayed stable through week 36. This means that the total amount of vitamin D matters more than how frequently you take it.

The study found that vitamin D levels rise quickly at first and then stabilize. This pattern was consistent across all three dosing schedules, suggesting that the body reaches a balance point where it maintains a certain vitamin D level regardless of dosing frequency. The study also showed that even the smallest daily dose (7,000 IU) was sufficient to achieve healthy vitamin D levels when taken consistently, which is important because it suggests people don’t need large doses to get results

Previous research has suggested that different vitamin D dosing schedules might work, but this is one of the first studies to directly compare three realistic approaches in the same group of people. Most earlier guidelines recommended either daily or weekly dosing, but this study adds evidence that every-other-week dosing also works. The findings support the idea that healthcare providers have flexibility in recommending vitamin D replacement strategies

The study had several limitations worth noting. First, it included only 60 people, which is a relatively small number for a research study. Second, all participants were from one city in Armenia, so the results might not apply to people in other countries or climates where sun exposure differs. Third, the study was 80% female, so we can’t be certain the results apply equally to men. Fourth, researchers didn’t verify whether people actually took their supplements as instructed, which could have affected the results. Finally, the study didn’t look at long-term outcomes beyond 36 weeks or whether people experienced any side effects from the different dosing schedules

The Bottom Line

If you have low vitamin D levels, talk to your doctor about supplementation. Based on this research, you have three evidence-based options: (1) taking a small dose daily, (2) taking a medium dose once weekly, or (3) taking a larger dose every other week. All three approaches work equally well to restore healthy vitamin D levels within 12 weeks. Choose the option that fits best with your lifestyle and ability to remember to take supplements. Confidence level: Moderate (this study is well-designed but relatively small and limited to one population)

This research is most relevant for adults with confirmed vitamin D deficiency who need supplementation. It’s particularly useful for people who struggle with daily pill routines and want to know if less frequent dosing works just as well. Healthcare providers in Armenia and similar climates should find this especially helpful. However, the findings may not apply to children, pregnant women, people with certain medical conditions affecting vitamin D absorption, or those taking medications that interact with vitamin D

You can expect to see meaningful improvements in your vitamin D levels within 4 weeks of starting supplementation. By 8 weeks, your levels should reach healthy ranges. The benefits continue to stabilize through 12 weeks, after which your vitamin D levels should remain stable as long as you continue taking supplements

Want to Apply This Research?

  • Track your vitamin D supplementation schedule by logging each dose taken (daily, weekly, or every-other-week depending on your chosen regimen). Record the date, time, and dose amount. If possible, note any symptoms of deficiency you’re experiencing (fatigue, muscle weakness, bone pain) to monitor improvement over the 12-week period
  • Choose your preferred dosing schedule based on your lifestyle, then set up reminders in your app to match that schedule. If you choose daily dosing, set a daily alarm. For weekly dosing, set a reminder for the same day each week. For every-other-week dosing, set a reminder every 14 days. This removes guesswork and helps ensure consistency
  • Log your supplement intake consistently for the full 12 weeks to track adherence. After 12 weeks, ask your doctor to recheck your vitamin D blood levels to confirm you’ve reached healthy ranges. Continue logging your supplements long-term to maintain healthy vitamin D levels. If you notice symptoms returning (fatigue, weakness), this signals you may have missed doses and need to refocus on consistency

This research summary is for educational purposes only and should not replace professional medical advice. Vitamin D supplementation needs vary based on individual health conditions, medications, age, and other factors. Before starting any vitamin D supplement regimen, consult with your healthcare provider to determine the appropriate dose and schedule for your specific situation. This study was conducted in Armenia and may not apply equally to all populations. If you have concerns about your vitamin D levels or experience symptoms like persistent fatigue, muscle weakness, or bone pain, seek evaluation from a qualified healthcare professional.