In Part 1, we discussed what HbA1c is and why you should keep it at healthy levels. In this post, we discuss 33 lifestyle factors, hormones, foods, and supplements that can affect HbA1c levels.

HbA1c 2-Part Series

Lifestyle Factors that Elevate HbA1c

1) Smoking

Higher HbA1c levels were found in smokers in six studies [1, 2]. HbA1c was 0.1% higher in current smokers and 0.03% higher in ex-smokers, compared with those who never smoked [1].

Smoking is also associated with unsatisfactory blood sugar levels in diabetics. Both type 1 and type 2 diabetes patients who smoked had higher HbA1c values than non-smokers [3].

Among women with gestational diabetes, HbA1c was higher than expected in women who smoked at the beginning of the pregnancy [2].

2) Opiates and Substance Abuse

Chronic opiate use has been reported to increase HbA1c levels, but the exact mechanism remains unknown [4].

HbA1c level was elevated in patients with substance abuse [5].

3) Low Temperature

Cold weather may increase HbA1c levels in people with type 2 diabetes. For every 1°C decrease in temperature, there was an increase in the risk of having an HbA1c level >7% [6].

Additionally, diabetic patients were at higher risk of having HbA1c over 7% in the winter and spring than in the summer [6].

4) Psychological and Social Factors

Mood difficulties are common among patients with diabetes and are linked to poor blood glucose control and increased diabetes complications [7, 8].

Studies indicate an association between behavior problems (internalizing, externalizing) and HbA1c levels in youth with type 1 diabetes. Increased problematic behaviors in youth with type 1 diabetes are associated with elevated HbA1c and mediated by low self-confidence and diabetes mismanagement [9].

Lower life satisfaction is associated with higher HbA1c [10].

Weight discrimination is associated with higher HbA1c in obese people, in addition to the effects of obesity on HbA1c itself, suggesting that psychological and social factors can increase vulnerability to diabetes in nondiabetic subjects [11].

5) Air Pollution

Long (1-year) and intermediate (3 months) term exposure to higher concentrations of air pollution was associated with increases in HbA1c [12, 13, 14, 15].

Air pollution was associated with higher HbA1c levels in newly diagnosed type 2 diabetes patients [16].

6) Electromagnetic Radiation

Radiofrequency electromagnetic field radiation (RF-EMFR) generated by mobile phone base stations increased HbA1c in school students who were exposed to high RF-EMFR. Moreover, students who were exposed to high RF-EMFR had a significantly higher risk of type 2 diabetes mellitus relative to their counterparts who were exposed to low RF-EMFR [17].

Because this study involves a small sample size (159 students) and is an observational study, more studies would be necessary to confirm that EMF really causes higher HbA1c.

Drugs that Increase HbA1c

7) Statins

The use of high-potency statins may increase HbA1c levels in patients with or without diabetes [18]. In patients with diabetes, HbA1c increased by 0.4% after high-potency statin use [18].

There is an increased risk of new-onset diabetes with statin use [18].

The effects, though, may vary by drug. HbA1c was significantly increased after 3 months in patients receiving atorvastatin, while levels remained unchanged in those receiving pitavastatin [18].

How to Decrease HbA1c

You can request from your doctor to test your HbA1c. Conventional doctors will look at a high HbA1c level and not mention anything. Sometimes, a lab result may be in the reference range, but not actually be in the optimal range. Reference ranges are not the same as an optimal range. This is why HbA1c even in the ‘normal’ range can be unhealthy and indicate that certain processes in the body aren’t optimal.

Lifestyle Factors that Decrease HbA1c

1) Exercise

In adults at moderate or high risk for type 2 diabetes, higher amounts of moderate to vigorous physical activity were associated with lower HbA1c. In this study, physical activity was more beneficial in shorter bouts of ≥10min [19].

Regular exercise also decreased HbA1c in healthy women [20].

In children and adolescents with type 1 diabetes, a higher degree of physical activity was associated with lower HbA1c [21]. One study showed that after acute exercise, mean HbA1c can increase in type 1 diabetic athletes. However, in the long term, HbA1c decreases [22].

Exercise also lowered HbA1c in individuals with type 2 diabetes [23]. Aerobic exercise, resistance training, and both combined were each associated with declines in HbA1c levels in type 2 diabetics [24, 25]. A systematic review showed that exercise of more than 150 minutes per week reduced HbA1c efficiency more than 2 times as compared to 150 minutes or less of exercise per week [25].

In another study, both resistance or treadmill exercises caused a reduction in HbA1c values. However, the greater reduction was noted with resistance exercise. Ten weeks of resistance exercises were associated with significantly better blood sugar levels in adults with type 2 diabetes compared to treadmill exercise [26]. Resistance exercise may improve HbA1c levels by improving the storage and utilization of glucose in muscles [26].

Exercise, however, did not improve HbA1c in type 2 diabetic patients with more serious vascular complications [27].

2) Socio-economic factors

Higher socio-economic status or high levels of parental education were found to be associated with lower HbA1c in children and adolescents with type 1 diabetes [28].

Caucasian, higher socioeconomic status, two-parent household, more frequent self-monitoring of blood glucose and low insulin requirements were associated with lower HbA1c concentration one year after the onset of type 1 diabetes in children [29].

These factors probably translate into HbA1c levels through increased diet quality, less stress, and more exercise.

3) Emotions

Emotional regulation and emotional intelligence may affect blood sugar levels in adults with type 2 diabetes. Lower HbA1c levels were significantly associated with less affect intensity and with higher emotional intelligence in type 2 diabetes patients. Therefore, interventions that can reduce affect intensity and/or increase emotional intelligence may improve blood sugar levels in adults with T2 diabetes [30].

Mindful self-compassion training significantly reduced depression, diabetes distress, and HbA1c. These results were maintained at a 3-month follow-up. This report suggests that learning to be kinder to oneself (rather than being harshly self-critical) may have both emotional and metabolic benefits among patients with diabetes [7].

4) Sleep

Sleep duration and the number of sleep segments are associated with HbA1c in type 2 diabetes patients. A one-hour longer sleep duration was associated with a 0.174% (1.4 mmol/mol) decrease in HbA1c. Moreover, participants who napped had lower HbA1c [31].

In type 2 diabetes subjects, later bedtime on weekends was significantly associated with poorer glycemic control [32]. In another study, in type 2 diabetes patients, sleep compensation during weekends (sleep duration of about 1h more during weekends compared to weekdays) had a beneficial effect on HbA1c [33].

Adults with type 1 diabetes who reported sleeping >6 hours had lower HbA1c levels than those sleeping ≤6 hours. Similarly, subjects reporting good sleep quality had lower HbA1c than those with poor sleep quality [34].

In patients with type 1 diabetes, social jetlag, a small but recurrent circadian misalignment between biological and social time, was associated with higher HbA1c [35].

Another study showed that both short (<5h) and long (>9h) sleep durations were associated with an increased HbA1c in type 2 diabetes patients. So was poor sleep quality [36].

5) Blood donation

HbA1c decreases after donating blood. Therefore, HbA1c levels are likely to be underestimated after blood donation in patients with diabetes mellitus [37].

6) Alcohol

Moderate alcohol consumption can reduce HbA1c in both non-diabetics [38] and diabetics [39].

Higher alcohol intake was associated with lower HbA1c levels in Korean adults [40].

In Japanese women, HbA1c levels were lower in occasional, regular light and regular heavy drinkers than in nondrinkers. HbA1c was further significantly lower in regular light and heavy drinkers than in occasional drinkers [41].

Higher alcohol consumption was associated with lower HbA1c in diabetes patients [39].

Nutritional Factors that Decrease HbA1c

7) A Healthy Diet

Intake of vegetables and fruits can reduce HbA1c [42].

A study showed that in nondiabetics, for every extra 80 g vegetable portion consumed, HbA1c reduced by 0.01% [43].

Mediterranean Diet

Mediterranean diet has beneficial effects on diabetes and lowers HbA1c [44, 45].

Mediterranean diet includes healthy components, such as fruits, vegetables, nuts, legumes, whole grains, fish and moderate intakes of red wine. All these contain essential nutrients and health-promoting properties, including high fibers, high magnesium, high anti-oxidant and high mono-unsaturated fatty acids (MUFA) [45].

Compared with the usual diet, a traditional Cretan Mediterranean diet lowered HbA1c from 7.1% to 6.8% in type 2 diabetics [46].

In overweight middle-aged men and women with newly diagnosed type 2 diabetes, a low-carbohydrate Mediterranean diet resulted in a greater reduction of HbA1c levels, a higher rate of diabetes remission, and delayed need for diabetes medication compared with a low-fat diet [47].

Another study found that the Mediterranean diet reduced HbA1c significantly compared to the usual diet, but so did the Paleo diet [48].

Paleo Diet

In type 2 diabetes patients, a Paleo diet consisting of lean meat, fruits, vegetables and nuts, improved HbA1c and glucose and lipid profiles [49, 50].

8) Protein-rich Meals

When an energy-restricted, protein-rich meal was used to replace certain meals in obese type 2 diabetes patients, over a period of 12 weeks, HbA1c decreased from 8.8% to 8.1%. Participants who continued with the practice further reduced their HbA1c [51].

9) Carbohydrate Restriction

A loose restriction of carbohydrate intake in type 2 diabetes patients during the 2-year follow-up period, improved HbA1c levels significantly [52].

A low carbohydrate diet reduced HbA1c and BMI in Japanese patients with poorly controlled type 2 diabetes [53].

10) Fiber

Higher total fiber intake was associated with lower HbA1c in type 1 diabetes patients [54].

HbA1c levels were lower in patients consuming more fiber. Increasing fiber intake may be an effective approach to improve blood sugar levels in type 2 diabetic patients [55, 56].

11) Probiotics

A probiotic strain, L. fermentum reduced HbA1c in clinically asymptomatic volunteers with borderline-high values [57].

Multistrain probiotics and probiotic yogurt decrease HbA1c in people with type 2 diabetes [58, 59, 60, 61].

Some studies, however, failed to find improvement associated with probiotics [62, 63].

12) Plain Water

A study showed that 1 cup of plain water per day was associated with a -0.04% lower HbA1c in men. Men had a 22% reduced odds of having HbA1c≥5.5% for each cup per day of plain water. There was no such association in women, however [64].

13) Carotenoids

In a follow-up survey, tracking non-diabetics over 10 years, carotenoids were significantly associated with lower HbA1c levels. Regular intake of carotenoids from supplements and medications was associated with a lower increase in HbA1c levels. Furthermore, this relationship was observed in those who never smoked but not in former and current smokers [65].

Lycopene, given as an adjunctive treatment in periodontal (gum) therapy, effectively reduced HbA1c [66].

14) Vitamin D

An association was found between higher HbA1c levels and lower Vitamin D in pregnant women [67].

Vitamin D administration decreases HbA1c levels in children and adolescents with type 1 diabetes [68].

Enhanced vitamin D supplementation also improves HbA1c in type 2 diabetes overweight and obese patients [69].

However, other studies in healthy subjects found no correlation between vitamin D and HbA1c [70, 71].

15) Magnesium

Low blood magnesium levels in children and adolescents with type 1 diabetes are associated with higher HbA1c and increased the risk of unsatisfactory blood sugar levels [72].

16) Chromium

In newly diagnosed patients with type 2 diabetes, lower blood chromium concentration was associated with higher HbA1c values [73].

In newly onset patients with type 2 diabetes, chromium supplementation improved HbA1c values significantly from 9.51% to 6.86% indicating better blood sugar levels [74].

Based on the NHANES study for the years 1999 – 2010, compared with nonusers, the odds of having type 2 diabetes (HbA1c ≥6.5%) were lower in persons who consumed chromium-containing supplements within the previous 30 d than in those who did not [75].

Some studies, however, found no association between chromium and HbA1c, and argue against using this supplement in diabetes [76].

17) Curcumin

A 9-month curcumin intervention in a prediabetic population significantly lowered the number of prediabetic individuals who eventually developed type 2 diabetes, significantly lowering HbA1c [77].

In type-2 diabetic patients, nano-curcumin significantly decreased HbA1c [78].

Moderate curry consumption marginally decreased HbA1c in young males [79].

18) Oats

Oats can decrease HbA1c and fasting glucose. The intake of oats and beta-glucan extracted from oats tends to lower HbA1c. Higher consumption of whole oats and oat bran, but not oat or barley beta-glucan extracts, are associated with lower HbA1c, fasting glucose and fasting insulin of in type 2 diabetes, overweight subjects with elevated cholesterol and TG levels [80].

19) Dark Chocolate

Among type 1 diabetes patients, those who consumed dark chocolate (25 g/day 2 – 5 times/week) showed a significantly lower HbA1c than both patients who consumed the same amount of milk chocolate or neither dark nor milk chocolate [81].

In another study, patients who ate up to 2 – 6 servings (28.5 g) of dark chocolate per week had a 34% lower risk of being diagnosed with diabetes [82].

20) Ginseng

An 8‐week treatment with ginseng extract moderately improved HbA1c levels and was well tolerated in type 2 diabetic patients with inadequate blood sugar levels [83].

Other studies reveal no significant difference in HbA1c levels in ginseng supplementation but show that ginseng improved fasting glucose, insulin resistance, triglycerides and cholesterol [84].

Hormones/Pathways that May Decrease HbA1c

21) Adiponectin

Higher levels of adiponectin are associated with a lower risk of developing type 2 diabetes [85, 86]. Higher adiponectin levels were also associated with lower HbA1c in nondiabetics [85].

Conversely, in patients with type 1 diabetes, an association between elevated blood adiponectin concentration and high HbA1c has been reported [87].

However, other studies found that concentrations of adiponectin were not correlated with levels of HbA1c in the diabetic and non-diabetic subjects examined [88, 89].

More studies are needed to clarify the relationship between adiponectin and HbA1c.

22) Thyroid Hormone

Elevated HbA1c was found in non-diabetic hypothyroid (low thyroid hormone) patients. Hypothyroid patients often show anemia which is another condition showing falsely elevated HbA1c [90, 91].

Also, the thyroid hormone increases the production of new red blood cells, another condition that results in lower HbA1c [92].

Drugs that Decrease HbA1c


23) Drugs that Destroy Red Blood Cells

Any drug which causes the rupture or destruction of red blood cells can potentially lower HbA1c by increasing the proportion of younger cells in the blood. Dapsone, ribavirin, antiretroviral, and sulfonamide drugs have all been reported to reduce the HbA1c in this manner [4].

24) Aspirin

Chronic use of aspirin has been reported to falsely decrease HbA1c [4]. However, aspirin can also modestly, in a way that is not clinically relevant, increase HbA1c levels in some cases [93].

25) Hydroxyurea

Hydroxyurea is used for the treatment of some leukemias and sickle cell disease. This drug can significantly reduce the number of blood cells and causes a decrease in HbA1c levels [4].


  • Higher PCSK9 levels are associated with higher HbA1c in patients with type 2 diabetes but not in patients without type 2 diabetes [94]. PCSK9 is important because it decreases the degradation of LDL cholesterol. High PCSK9 means more LDL cholesterol.
  • Resistin is associated with HbA1c in non-diabetic but not diabetic obese individuals [95].
  • Higher uridine was associated with higher HbA1c in children with type 1 diabetes [96].
  • A strong correlation between creatinine and HbA1c was observed in subjects with impaired glucose tolerance [97].
  • TNF-alpha may mediate the positive effect of exercise on HbA1c levels [20].

Irregular HbA1c Levels?

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HbA1c 2-Part Series

About the Author

Biljana Novkovic - PHD (ECOLOGICAL GENETICS) - Writer at Selfhacked

Dr. Biljana Novkovic, PhD

PhD (Ecological Genetics)

Biljana received her PhD from Hokkaido University.

Before joining SelfHacked, she was a research scientist with extensive field and laboratory experience. She spent 4 years reviewing the scientific literature on supplements, lab tests and other areas of health sciences. She is passionate about releasing the most accurate science & health information available on topics, and she's meticulous when writing and reviewing articles to make sure the science is sound. She believes that SelfHacked has the best science that is also layperson-friendly on the web.

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