Multiple factors contribute to weight gain. While some of them are known such as caloric surplus, others are widely overlooked. Nutrition has a major impact on our weight. We usually associate an unhealthy diet with weight gain, but healthy nutrients can also make it happen and in this post, we are going to focus on vitamins. Scroll down to learn more about vitamins and weight gain.

Can Vitamins Cause Weight Gain?

The role of vitamins in potential weight gain is not extensively studied, but current evidence confirms the link exists. For example, the World Journal of Diabetes published a review that focused on the role of vitamins in obesity, especially excess vitamin intake. The paper explains that excess vitamin intake is an unrecognized risk factor for obesity. Scientists identify the daily intake of vitamins as the main reason behind excessive levels of these micronutrients. 

Back in time, vitamins were obtained solely through natural foods and seasonal changes in diet. The intake of fresh vegetable-derived vitamins was higher in summer than in winter. Through evolution, humans have adapted to the seasonal variations in vitamin consumption by developing mechanisms to maintain vitamin homeostasis (balance). 

The study also explains the body can store a certain amount of vitamins when the supply is adequate and use it in times when then the intake is insufficient. For that reason, it seems unnecessary to take vitamins every day. Our body needs a specific amount of vitamins to function properly. But over the past several decades the actual intake of vitamins has been significantly higher than the estimated daily average requirements due to:

  • Out-of-season cultivation
  • Increased vitamin intake from animal sources
  • Higher vitamin intake from artificial sources such as food fortification, vitamin-enriched drinks

As a result, we tend to consume greater amounts of some vitamins than our body actually needs during the day. Excess vitamins may contribute to weight gain by contributing to insulin resistance, enhancing fat synthesis, and disturbing metabolism (1).

The same journal published a different study that examined the vitamin paradox in obesity and tried to uncover whether we lose weight due to deficiency or excess. Scientists explained that excessive vitamin intake can lead to a vitamin paradox where people gain weight. This happens due to several reasons including:

  • Increased reactive oxygen species (ROS) generation and subsequently leading to oxidative tissue damage and insulin resistance
  • Disturbance of the degradation of neurotransmitters and hormones by competing for drug-metabolizing enzymes and detoxification resources 
  • Epigenetic changes, e.g. altered DNA methylation, by depleting the body’s methyl-group pool

This means that excessive vitamin intake, e.g. through high consumption of fortified foods, can deplete the drug-metabolizing system, which is manifested through high levels of unmetabolized vitamins. It can also harm the antioxidant system and eventually cause various metabolic disorders and oxidative tissue damage. These processes play a causal role in the increased prevalence of obesity and related conditions. What’s more, scientists theorize that obesity could be one of the manifestations of chronic vitamin poisoning, in some cases. Vitamin poisoning is dose-dependent and occurs in cases when high levels of certain micronutrients are consumed (2).

Vitamins That May Cause Weight Gain

As seen above, vitamins can lead to weight gain. This happens when higher amounts of vitamins are consumed. But some are more likely to contribute to weight gain than others. Below is the rundown of vitamins that may contribute to putting on a few pounds.

1. Vitamin A

Vitamin A is a fat-soluble vitamin involved in a wide range of functions. The body needs vitamin A for vision, immune function, cellular communication, and reproduction. This micronutrient also supports cell growth and differentiation thus playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs (3).

Consumption of vitamin A is important for our general health and wellbeing. However, some people may experience weight gain. A study from the Experimental Physiology evaluated the impact of vitamin A on weight in lean and glucose-intolerant rats. Findings showed that a vitamin A-enriched diet aggravated weight gain and adiposity or obesity in both lean and glucose-intolerant animals. More precisely, consumption of vitamin A for 14 weeks led to increased body weight, weight gain, and visceral adiposity but further studies are necessary to uncover mechanisms underlying these effects (4). 

One potential mechanism of action is that vitamin A can elevate the presence of PPARγ (peroxisome proliferator-activated receptor-gamma), highly expressed in white adipose tissue. The expression of this receptor is associated with higher levels of leptin. Leptin is a hormone produced by the body’s fat cells and it is referred to as “satiety hormone” or “starvation hormone”. Since fat cells produce leptin in proportion to their size, obese or overweight men and women tend to have high levels of this hormone (5).

2. Vitamin B Complex

B-complex vitamins play a crucial role in maintaining good health and wellbeing. These micronutrients have a direct impact on brain function, energy levels, and cell metabolism. Production of red blood cells requires B-complex vitamins and you also need them for cardiovascular health, good appetite, production of hormones and cholesterol, among other things (6). 

The relationship between excessive intake of B-complex vitamins and weight gain is scientifically confirmed, but more research is necessary to learn more about it. 

A study from Health Promotion Perspectives examined the role of B vitamins in weight disorders among children and adolescents, aged six to 18 years. The findings showed an association between the consumption of these micronutrients and weight disorders. According to these findings, intake of vitamin B1 (thiamine), B3 (niacin), B5 (pantothenic acid), and B6 (pyridoxine) potentially contributes to weight-related problems (7). Since there are several forms of vitamin B, we’re going to focus on some of them individually below.


Higher amounts of thiamine intake can contribute to weight gain increasing food consumption, according to a study from the Neuroscience journal (8). Don’t think of it as a bad thing. In fact, this can help people who are underweight to gain more pounds and protect their health. 

Weight gain due to higher thiamine consumption could be down to the upregulation of AMP-activated protein kinase (AMPK), which is a biochemical food intake regulator. Increased levels of thiamine can increase the expression of AMPK and further contribute to weight gain.


For example, a study from the World Journal of Gastroenterology found that excess intake of niacin is a risk factor for obesity in U.S. children. Compared to control oral glucose tolerance tests and insulin levels were higher after co-administration of glucose and niacin. The same study also elaborated that the prevalence of obesity among American children increased with the higher per capita niacin consumption. This happens due to the wide prevalence of products and foods fortified with niacin (9). The role of niacin in weight gain could be attributed to the glucose-controlling hormone, including insulin. Excessive consumption of niacin may decrease serum glucose concentration and potentially alter food intake behavior. Additionally, niacin could be considered as an appetite stimulator. 


The results of a study that enrolled children and adolescents also showed that boys receiving further amounts of vitamin B2 (riboflavin) and man-made form of vitamin B12 (cyanocobalamin) had higher BMIs. These findings only confirm the results of other studies that linked B-complex vitamins to weight gain. 

When it comes to this micronutrient, a large study from the European Journal of Nutrition investigated associations between nutrient patterns and weight changes in adults. The study included 235,880 participants, 25-70 years old, from 10 European countries. The subjects were followed between 1992 and 2000. Mean weight gain was 460 g/year for men and 420 g/year for women. The study showed that higher consumption of riboflavin, alongside phosphorus, protein, and calcium was associated with weight gain (10). The positive link between riboflavin and weight gain could be attributed to lowered apoptosis of adipocytes. Higher levels of riboflavin can increase lipogenesis and lipid accumulation while decreasing free fatty acid release. Reminder, lipogenesis is a process of fatty acid and triglyceride synthesis from glucose and substrates. 

B-complex vitamins pyridoxine and pantothenic acid can also contribute to weight gain. Pyridoxine, as a cofactor, is involved in biosynthesis reactions that transform proteins into fats. That’s why excessive intake could contribute to weight gain. 

Folic Acid 

Vitamin B9 (folic acid) is crucial for our health and wellbeing, especially in pregnancy. Consumption of this vitamin has increased to high levels in many countries which raised concerns about potential adverse reactions. Some of these side effects may include disturbances to energy and lipid metabolism. 

A study from the journal Nutrients aimed to investigate the impact of folic acid on metabolic function in a rodent model. Results showed that rats fed excess folic acid and a high-fat diet had significantly greater weight gain than their counterparts fed adequate folic acid. Just like with the above-mentioned vitamin A, excess folic acid was associated with increased expression of PPARγ, which could explain why it can contribute to weight gain (11).

3. Vitamin E

Vitamin E is a fat-soluble vitamin known for powerful antioxidant effects. Besides antioxidant properties, vitamin E is also involved in immune function, cell signaling, regulation of gene expression, and other metabolic processes (12). 

Its potential to neutralize free radicals and oxidative stress makes vitamin E a staple ingredient in the beauty and skincare industry. 

The role of vitamin E in weight gain is poorly elucidated, the same as with other vitamins. However, evidence shows that excess vitamin E could, indeed, lead to weight gain. The vast majority of research on this topic was carried out on the rat model. 

Rats fed with a normal rat food diet showed a progressive increase in weight until they were two years old. However, for quite some time the scientists didn’t look for the nutritional content of that diet and whether some nutrients contributed to weight gain more than others. That being said, one study found that the increase in weight after a period of time wasn’t observed in animals given a vitamin E-deficient diet. These findings indicate vitamin E can cause weight gain. The potential mechanism could be that vitamin E slows metabolism thus creating a fertile ground for fat accumulation (13). 

How to Avoid Weight Gain?

Overweight and obesity are widely prevalent. According to the CDC, 71.6% of adults aged 20 and older are overweight or obese in the United States (14). We can gain weight due to a number of reasons including a sedentary lifestyle, certain health conditions, unhealthy diet, among other things. 

Throughout this post, we’ve covered some vitamins that are also associated with increased body weight. Now you’re probably wondering whether these vitamins are safe for you. If you struggle to maintain weight in a healthy range or you’re on the road to slim down, you don’t want vitamins that cause an obstacle. 

While the studies have shown some vitamins can cause weight gain, you need to keep in mind excessive amounts are involved. You’re not likely to gain weight when you consume adequate amounts of vitamins or stay within recommended daily intake. 

Therefore, the key here is to avoid taking too much of the vitamins mentioned above. We tend to think the more we eat, the greater the effects are. But it doesn’t work like that. The body needs specific, moderate amounts of nutrients. These limits exist because they allow the body to function properly and it gets to absorb and metabolize them effectively. 

Should You Avoid Supplements and Fortified Foods?

Figures show that 77% of U.S. adults take dietary supplements. Vitamins and minerals are the most commonly consumed supplement category (15). Fortified foods and dietary supplements have become widely accessible. The main intention behind these products is to provide adequate amounts of different nutrients and micronutrients to prevent deficiencies. Since an unhealthy diet is widely prevalent it has become difficult for most people to obtain sufficient amounts of various nutrients from diet alone. 

However, a high intake of some vitamins can cause weight gain. If you take supplements daily or eat fortified foods, you may think you should avoid them. It doesn’t have to be like that. Read labels carefully to see the amounts of these vitamins. Make sure to adjust your diet accordingly to avoid consuming excess vitamins. You may consult a dietitian or a nutritionist to help you out. 

If You Are Underweight, Should You Take More Vitamins?

Studies that explored the relationship between vitamins and weight gain found that excess intake was the main culprit. High, long-term consumption caused a chain of reactions that culminated with weight gain. For underweight men and women, this may seem like a convenient way to put on a few pounds. 

However, you should avoid doing so without consulting your doctor. Even more so if you’re already taking medications for a certain health condition. Healthcare providers will recommend useful solutions and strategies to gain weight. 


We usually think vitamins are healthy so it’s okay to consume high amounts. The more we eat, the better our health will get. That’s a common mistake that most of us make. Studies show that excess intake of various vitamins can lead to weight gain due to impaired metabolism, fat accumulation, increased expression of receptors, among other things. Modify your diet so that the intake of vitamins is sufficient, not excessive. Consult your doctor if you’re underweight. 

















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