Vitamin D and Wegovy: does semaglutide affect your levels?

Does Wegovy actually reduce vitamin D absorption?

Not directly. Semaglutide works by activating GLP-1 receptors in the brain and gut, which reduces appetite, slows gastric emptying and lowers calorie intake. Vitamin D absorption relies primarily on dietary fat (it is fat-soluble) so as long as you are still eating some fat with meals, the mechanism for absorbing vitamin D remains intact. The NHS medicines page for semaglutide does not list vitamin D depletion as a recognised side effect of Wegovy.

The real concern is indirect. On Wegovy, many people eat considerably less and naturally reduce fatty foods in particular. Fewer oily fish, fewer eggs, less fortified food, these are among the main dietary sources of vitamin D in the UK. Over months, that reduced intake can quietly push levels lower, especially in autumn and winter when sunlight synthesis is poor anyway. If your levels were already borderline before starting treatment, that matters more.

There is also the broader context of obesity itself: adipose tissue sequesters vitamin D, so people with higher body weight tend to have lower circulating levels at baseline. As you lose weight on Wegovy, some of that stored vitamin D may be released, which is one reason the picture is not straightforward. Our guide to vitamins to take when on Wegovy explains how to approach supplementation given all these competing factors. A blood test is the only reliable way to know where you actually stand.

How common is vitamin D deficiency in people starting Wegovy?

Quite common, as it turns out. Public Health England estimated that around one in five adults in the UK has low vitamin D levels, and that figure skews higher among people living with obesity. The NHS healthy weight guidance acknowledges that nutritional status is worth monitoring when dietary patterns change substantially, and starting a GLP-1 medicine represents exactly that kind of change.

For UK residents specifically, the government already recommends that everyone considers a 10 micrograms (400 IU) daily supplement between October and March, when sunlight is insufficient for skin synthesis. People with darker skin tones, those who cover most of their skin outdoors, or anyone who spends limited time outside are advised to supplement year-round. If you fall into any of those groups and are also eating less on Wegovy, it is worth raising at your next clinical review rather than waiting for symptoms to appear.

Symptoms of deficiency (fatigue, low mood, muscle weakness, bone discomfort) can be vague and easy to attribute to other causes, including the early weeks of treatment adjustment. A GP can request a simple 25-hydroxyvitamin D blood test if you are unsure.

Should you take a vitamin D supplement while on Wegovy?

For most people in the UK, a standard 10 microgram (400 IU) daily supplement is low-risk and inexpensive. The NHS recommends this for broad population groups regardless of medication, so adding one during Wegovy treatment is unlikely to require much deliberation. Higher doses (sometimes prescribed for confirmed deficiency) should be guided by a blood test result rather than self-prescribed, because vitamin D toxicity, while uncommon, is a real risk at sustained high doses.

Timing is straightforward: take vitamin D with a meal that contains some fat. If you are already planning your doses around the tablet-before-breakfast rule that applies to some other medications, a vitamin D capsule works well at lunch or dinner instead. It does not need to be separated from your weekly Wegovy injection in any specific way.

Our guidance on which vitamins to consider when on Wegovy covers the wider picture beyond vitamin D, including what to prioritise if appetite suppression is significant. If you want to understand how semaglutide affects other nutrients, the relationship between semaglutide and vitamin B12 is worth reading alongside this.

What should you actually do about vitamin D on Wegovy?

Start by checking whether you are already supplementing. Many people are not, even outside of weight management treatment. If you are not, adding a standard 10 microgram supplement is a sensible baseline. If you have symptoms that might suggest deficiency (persistent fatigue, low mood through winter, aching joints) ask your GP for a blood test before deciding on a higher dose.

At your Wegovy reviews, mention your vitamin D status alongside anything else you are taking. Our prescribers note that questions about nutrient status come up regularly in repeat consultations, and there is no downside to raising it. You can also read our broader overview of Wegovy and vitamins for a fuller picture of nutritional considerations during treatment.

For anyone already on treatment and wondering whether to adjust their supplement regime (perhaps after a holiday where sun exposure was higher, or ahead of a winter without much daylight) it is worth timing a conversation with your clinical team around those seasonal shifts. A winter review is often the right moment. The best vitamins to take alongside Wegovy varies slightly by individual, which is why a prescriber's input matters. If you have broader questions about getting started, our frequently asked questions page covers the consultation process in detail.