Frequent Cannabis Users Show Lower Vitamin D in Two Studies. The Cause Is Not Yet Known.
Two studies found lower vitamin D in people who use cannabis frequently. Here is what was measured, what was found, and where the evidence stops.
Two independent studies, conducted in different countries and different populations, have found that people who use cannabis frequently tend to have lower circulating vitamin D than people who do not. The finding is consistent enough to take seriously and limited enough that it should not be overstated. Neither study was designed to show that cannabis lowers vitamin D, and both leave open explanations that have nothing to do with cannabis itself. This article sets out what was measured, what was found, and where the evidence stops.
Why vitamin D status matters
Vitamin D is formed in the skin during exposure to ultraviolet B light and is also obtained from a small number of foods and from supplements. The liver converts it to 25-hydroxyvitamin D, written 25(OH)D, which is the circulating form measured in a standard blood test. The kidneys and other tissues then convert 25(OH)D to its active hormonal form, which regulates calcium absorption and acts on receptors found throughout the body. Results are usually reported in nanograms per milliliter (ng/mL), the unit used on most U.S. lab reports and throughout this article. Under the National Academies criteria, a level of 20 ng/mL or higher is generally considered adequate for bone and overall health, 12 to below 20 ng/mL is considered inadequate, and below 12 ng/mL is associated with deficiency.
Inadequate status is common well beyond any single group. In national survey data, 94 percent of people in the United States aged one and older consumed less vitamin D from food and beverages than the Estimated Average Requirement. Blood measurements from the same survey placed 18 percent of the population in the inadequate range and 5 percent in the deficient range. Any discussion of vitamin D in cannabis users therefore begins from a general population in which shortfalls are already widespread.
The Western Norway cohort
The larger of the two studies followed 666 adults receiving care in outpatient opioid agonist therapy clinics and municipal substance use clinics in Bergen and Stavanger, Norway, between 2016 and 2020. Researchers collected 1,887 serum 25(OH)D measurements, with most participants measured more than once over roughly two years. Weekly cannabis use in the preceding twelve months was reported by half of the cohort. Vitamin D shortfall was widespread across the group as a whole: 57 percent were below the 20 ng/mL adequacy threshold at their first measurement.
Among all the substances the researchers examined, cannabis was the only one associated with vitamin D status. Participants who used cannabis at least weekly had vitamin D levels about 2 ng/mL lower at the start than those with less or no use (statistical range roughly 0.5 to 3.6 ng/mL lower). That is a modest difference for an individual, but a consistent one across the group. Their levels did not decline further over the follow-up period. Weekly use of alcohol, benzodiazepines, stimulants, and non-prescribed opioids showed no significant association with vitamin D at baseline or over time. The analysis accounted for season, injecting, and opioid treatment dose, but it did not account for body mass index, dietary vitamin D intake, time spent outdoors, or skin type. The authors state directly that confounding is a threat in an observational design of this kind.
The bone health study
The second study, published in the American Journal of Medicine in 2017, compared regular cannabis smokers with tobacco smokers who did not use cannabis, all recruited from a single inner-city general practice in the United Kingdom. The study was approved by the South East Scotland Research Ethics Committee and NHS Lothian, and its authors are based at the University of Edinburgh, which places the practice in the Edinburgh area of Scotland. Its primary purpose was bone density, but it also measured serum 25(OH)D. Heavy users, defined as more than 5,000 lifetime episodes of cannabis smoking, averaged about 10 ng/mL, in the deficient range, compared with about 15 ng/mL in the control group, a statistically significant difference. Moderate users averaged about 14 ng/mL. It is worth noting that the control group itself averaged below the 20 ng/mL adequacy threshold.
The heavy-use group differed from controls in several ways beyond cannabis. Their age and sex distribution differed, their dietary calcium intake was lower, and about two-thirds had also used other illicit drugs. The paper does not report adjusting the vitamin D comparison for these differences, for season, or for sun exposure, and it offers no explanation for the vitamin D result. One detail runs against a common assumption: heavy users had a lower average body mass index than controls. Because higher body mass index is generally associated with lower 25(OH)D, excess body weight is unlikely to explain the lower vitamin D seen in this group. That point is an inference from the published figures rather than a conclusion the authors drew.
What these studies cannot tell us
Both studies observed people as they were; neither assigned cannabis use or controlled for the factors that most strongly determine vitamin D status. The most important of these is sunlight. People who spend more time indoors produce less vitamin D, and neither study measured time outdoors. Diet and economic circumstances are equally relevant. In the Norway cohort, 92 percent of participants relied on social benefits, and the small group in paid work had higher vitamin D than those on benefits, a pattern the authors attribute to differences in activity and sun exposure. Diet quality and daily routine in these populations are shaped strongly by income and circumstance, and the data cannot separate those influences from cannabis itself.
Geography matters as well, because latitude governs how much vitamin D the skin can make from sunlight. Both studies were conducted far to the north: Bergen and Stavanger lie at roughly 59 to 60 degrees north, and Edinburgh at about 56 degrees north, compared with about 42 degrees for Detroit or Chicago and 34 degrees for Los Angeles. The Norway data show how strongly season shapes status at those latitudes, with typical levels of about 22 ng/mL in summer falling to about 16 ng/mL in winter. Results from these settings cannot be assumed to carry over to people living at lower latitudes with more year-round sun.
The populations were also specific. The Norway findings come mainly from people in treatment for opioid use disorder, and 85 percent also smoked tobacco. The bone health study compared cannabis smokers with tobacco smokers from one practice. Neither group resembles the broad population of adults who use cannabis, including the growing number who use it medically. What the two studies do establish is a consistent association in two quite different settings. They do not establish that cannabis causes lower vitamin D, and the direction of the relationship remains unknown.
Where competition may enter: magnesium
A separate line of evidence concerns how the body processes the vitamin D it already has. The enzymes that convert vitamin D into 25(OH)D, and 25(OH)D into its active form, depend on magnesium, as does the protein that carries vitamin D in the blood. That dependence was established largely in laboratory and enzyme-level studies. A randomized, double-blind trial published in the American Journal of Clinical Nutrition in 2018 tested its relevance in people. Among 180 adults aged 40 to 85, magnesium supplementation raised 25(OH)D3 in participants whose baseline 25(OH)D was close to 30 ng/mL and lowered it in those with higher baseline levels. The authors concluded that adequate magnesium status may be important for optimizing vitamin D status, describing magnesium as a regulator of vitamin D metabolism rather than a simple booster.
This is where the concept of competition becomes useful. Magnesium serves hundreds of enzymatic reactions that draw on the same limited supply. The Solprana article Magnesium, Cannabis, and the Quiet Loss of Stability examines why regular cannabis use may increase the body’s demand for magnesium. If that is the case, vitamin D activation would be competing with other magnesium-dependent processes for a shared resource, in a population where most adults already fall short of recommended magnesium intake. This connection is a hypothesis that links separate findings. It has not been tested in cannabis users, and it should be read as a reason to study the question rather than as an established mechanism.
A note on the endocannabinoid system
There is early evidence that vitamin D and the body’s own cannabinoid signaling system are connected. In a 2020 study in mice, a vitamin D–deficient diet altered levels of the endocannabinoids anandamide and 2-arachidonoylglycerol in the gut and changed components of the endocannabinoid system in the spinal cord, alongside increased pain sensitivity. This finding comes from animals and does not show what happens in people. It does suggest that the two systems interact, and that the relationship between cannabis use and vitamin D may prove more complex than a simple loss of one nutrient.
What this means in practice
For anyone who uses cannabis regularly, the most reliable step is measurement rather than assumption. Serum 25(OH)D is a routine, inexpensive blood test, and the result places a person clearly within or outside the adequate range. Where intake needs to increase, vitamin D3 at intakes well within the adult Tolerable Upper Intake Level of 4,000 IU per day is the conventional approach, ideally alongside adequate magnesium given its role in vitamin D processing. Anyone taking anticoagulant medication should consult their healthcare provider before using a supplement that contains vitamin K2.
Happy Health Core was formulated with this pairing in mind. A daily serving provides 2,000 IU of vitamin D3, 120 mcg of vitamin K2 as MK-7, and 200 mg of magnesium as bisglycinate. No Solprana product has been tested in a controlled clinical trial, and supplementation complements rather than replaces testing and the guidance of a qualified healthcare provider.
Evidence summary
| Tier | Claim | Basis |
|---|---|---|
| HIGH | Most U.S. adults take in less vitamin D from food and beverages than the Estimated Average Requirement. | National survey data (NHANES), summarized by the NIH Office of Dietary Supplements. |
| MODERATE | Frequent or heavy cannabis use is associated with lower serum 25(OH)D. | Two observational studies in specific populations; not adjusted for sun exposure or dietary vitamin D. |
| MODERATE | Magnesium status influences how the body processes vitamin D. | One randomized trial (n = 180) plus enzyme-level laboratory work. |
| SPECULATIVE | A cannabis-related increase in magnesium demand could compete with vitamin D activation for the same magnesium supply. | Hypothesis connecting separate findings; not tested. |
| SPECULATIVE | Vitamin D status and endocannabinoid signaling interact in humans. | Animal data only. |
| NOT ESTABLISHED | Cannabis use causes vitamin D deficiency. | No study has tested this directly. |
References
Bemanian M, Chowdhury R, Stokke K, Aas CF, Johansson KA, Vold JH, Fadnes LT. Vitamin D status and associations with substance use patterns among people with severe substance use disorders in Western Norway. Sci Rep. 2022;12:13695.
Sophocleous A, Robertson R, Ferreira NB, McKenzie J, Fraser WD, Ralston SH. Heavy cannabis use is associated with low bone mineral density and an increased risk of fractures. Am J Med. 2017;130(2):214–221. doi:10.1016/j.amjmed.2016.07.034
Dai Q, Zhu X, Manson JE, Song Y, Li X, Franke AA, et al. Magnesium status and supplementation influence vitamin D status and metabolism: results from a randomized trial. Am J Clin Nutr. 2018;108(6):1249–1258. doi:10.1093/ajcn/nqy274
Uwitonze AM, Razzaque MS. Role of magnesium in vitamin D activation and function. J Am Osteopath Assoc. 2018;118(3):181–189. doi:10.7556/jaoa.2018.037
Guida F, Boccella S, Belardo C, Iannotta M, Piscitelli F, De Filippis F, et al. Altered gut microbiota and endocannabinoid system tone in vitamin D deficiency-mediated chronic pain. Brain Behav Immun. 2020;85:128–141. doi:10.1016/j.bbi.2019.04.006
National Institutes of Health, Office of Dietary Supplements. Vitamin D: Fact Sheet for Health Professionals. Accessed October 2026.
These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease. This article is for education and does not replace individual medical advice.
The finding is consistent enough to take seriously and limited enough that it should not be overstated.
This article is educational and is not medical advice. Solprana products are intended to complement, not replace, care prescribed by a qualified healthcare provider.