Algae are complex, photosynthetic organisms that constitute of multicellular macroalgae and unicellular microalgae.
It produces bioactive compounds that exhibit antibacterial, anti-inflammatory, antioxidant, and hypolipidemic properties.
There is growing interest in the use of algae as a supplement for its numerous health benefits.  
Key Health Benefits of Algae Supplements
The key benefits of algae supplements include modulating serum lipid markers, lowering blood pressure, and decreasing blood sugar levels. It may inhibit the proliferation and metastasis of cancer cells. Limited studies showed that it might enhance immune function, increase physical performance, reduce symptoms of allergic rhinitis, and improve cognitive function.
1. Algae supplements modulated serum lipid markers
Studies showed that algae supplements modulated serum lipid markers and may reduce the risk of cardiovascular diseases.
A meta-analysis showed that algal oil DHA administration reduced serum triglycerides and increased HDL cholesterol levels in persons without coronary artery disease.
1-2g of algal-DHA lowered plasma triglyceride levels in combination with statins. 
In patients with hyperlipidemic nephrotic syndrome, spirulina decreased triglyceride levels and LDL: HDL ratio.
1g of spirulina supplementation had a hypolipidaemic effect in dyslipidemic patients.  
A review of clinical trials showed that chlorella lowered serum total cholesterol and triglyceride levels. 
What it means: Several studies showed that algae supplements modulated the serum lipid markers. It increased triglycerides and total cholesterol levels. Future studies are required to determine if algae supplements reduced the risk of cardiovascular diseases by modulating serum lipid markers.
2. Algae supplements may lower blood pressure
Some studies showed that algae supplements might lower systolic and diastolic blood pressure.
4.5 g of spirulina reduced systolic and diastolic blood pressure in both men and women.
The spirulina supplementation reduced blood pressure in diabetic subjects with high triglyceride levels.
GABA rich chlorella supplements reduced diastolic blood pressure in subjects with borderline hypertension.  
Seaweed intake was inversely related to blood pressure. Girls with high seaweed intake had lower systolic blood pressure, whereas boys had lower diastolic blood pressure.
What it means: Algae supplements, including spirulina, chlorella, and seaweed, may have some beneficial effects on lowering blood pressure. Large randomized controlled trials will determine the mechanisms by which algae supplements reduce blood pressure.
3. Algae supplements may inhibit metastasis and proliferation of cancer cells
Several studies showed that algae supplements might inhibit migration, metastasis, and proliferation of cancer cells.
Astaxanthin, a pigment from microalgae, showed short term growth inhibition and cell death activity on breast cancer cell line, MCF-7. 
The compounds from seaweed inhibited growth and metastasis of breast cancer and colon cancer cells.
Oral leukoplakia subjects supplemented with spirulina showed a regression of oral lesions.
Spirulina may reduce burning sensation in oral submucous fibrosis patients without any side effects.
What it means: Several in vitro studies showed that algae supplements might reduce proliferation, metastasis, and induce apoptosis of cancer cells. Spirulina may reduce lesions and burning sensation in oral submucous fibrotic patients. More human studies with a better design in different populations are required to evaluate the anticancer properties of algae supplements.
4. Algae supplements may lower blood glucose levels
Studies showed that algal supplements, including blue-green algae and chlorella, may reduce blood glucose levels and improve glycemic status.
The supplementation of spirulina resulted in lowering fasting blood glucose and postprandial blood glucose levels in diabetic patients.
In another study, a spirulina supplement resulted in a 1% reduction in mean HbA(1c).
Chlorella supplementation improved glycemic status in patients with non-alcoholic fatty liver disease.
It reduced fasting glucose levels in subjects with high-risk factors for lifestyle-related diseases.
Eight-week supplementation of astaxanthin marginally reduced plasma glucose concentration.
What it means: Algae supplements may reduce blood glucose levels in patients with diabetes and improve glycemic status in non-alcoholic fatty liver disease. Further research findings will determine if algae supplements have the potential to manage diabetes.
5. Algae supplements may increase physical performance
Microalgae may increase physical performance and decrease fatigue in athletes requiring high levels of proteins.
In a randomized controlled trial, chlorella supplementation increased aerobic endurance capacity by enhancing peak oxygen uptake.
Spirulina supplementation in moderately trained males increased time to fatigue, fat oxidation rate, and exercise performance.
It decreased malondialdehyde, increased antioxidant enzymes, and reduced exercise-induced muscle damage.
Animal studies showed that astaxanthin might improve exercise performance and recovery.
But one human study showed that astaxanthin did not improve markers of muscle injury following the eccentric loading exercise.
What it means: Microalgae supplement, including spirulina and chlorella, may increase time to exhaustion and exercise performance in athletes. There is limited human research in supporting the use of astaxanthin, seaweed, and other algae supplements in enhancing exercise performance and, therefore, warrants further investigation.
6. Algae supplements may stimulate immune function
Microalgae supplements may stimulate the immune system by activating macrophages, natural killer cells, and modulating the release of proinflammatory cytokines.
In a study, chlorella derived supplement improved mucosal immune function by increasing the secretion of salivary SIgA. 
It increased the activity of natural killer cells, the serum concentration of interferon-gamma, and interleukin-12.
Spirulina supplementation for 12 weeks enhanced immune function in subjects higher than 50 years of age.
It activated macrophages, natural killer cells, and enhanced WBCs.
What it means: Microalga supplements, including chlorella and spirulina, may improve immune function. It may increase the activity of macrophages, natural killer cells, and enhance the secretion of antibodies. Further research studies are needed to elucidate the potential application of algae supplements to treat human pathological conditions through its immune-modulating properties.
7. Algae supplements may reduce the symptoms of allergic rhinitis
Algae supplements may reduce the symptoms of allergic rhinitis through its anti-inflammatory properties.
Allergic rhinitis is a mucosal inflammatory condition causing sneezing, nasal discharge, and obstruction of airflow.
A study involving 1002 Japanese pregnant women showed that a high intake of seaweed decreased the prevalence of allergic rhinitis.
In a double-blind, placebo-controlled study, the ingestion of spirulina improved nasal discharge, sneezing, nasal congestion, and itching in allergic rhinitis patients.
Another study showed that spirulina inhibited the inflammatory cytokine, IL-4, and modulated the symptoms of allergic rhinitis.
What it means: Research studies showed that algae supplement, including seaweed and spirulina, might reduce the symptoms of allergic rhinitis. Future studies will determine if algae supplements can be used as an alternate therapy for treating allergic rhinitis.
8. Algae supplements may improve cognitive function
Few research studies reported that algae supplements might improve cognitive function, including reaction time, spatial learning, and memory.
A randomized controlled study showed that brown seaweed extract improved accuracy on digit vigilance and choice reaction time tasks in healthy individuals.
Astaxanthin improved cognitive function in the aged population.
Fermented Spirulina extract showed memory-improving effects in mice, which may be due to antioxidant activities of beta carotene.
The supplementation of spirulina to protein malnourished mothers improved spatial learning and memory in offsprings. 
Chlorella supplementation improved short term memory and social behavior. 
What it means: Algae supplements may improve cognitive functions in individuals. Astaxanthin and chlorella showed preventing cognitive decline in the aging population. The human studies of algae supplement on cognition are limited and, therefore, warrants more studies.
9. Algae supplements may reduce body weight
Some algae supplements may reduce BMI and promote weight loss.
In a randomized controlled study, three months supplementation of spirulina reduced BMI and weight in patients with hypertension.
Ingestion of 2.8g os spirulina reduced body weight significantly.
Brown seaweed showed a more significant effect in reducing weight gain following eight weeks.
In a double-blind, randomized study involving obese women, the combination of brown algae fucoxanthin and pomegranate oil promoted weight loss.
What it means: Algae supplements, including spirulina and brown algae, may reduce body weight and BMI. More randomized controlled studies are required to examine the reliability of algae as weight loss supplements.
Precautions with Algae Supplements
Possible Side effects of Algae Supplements
Algae supplements that are free of contaminants are possibly safe when used for the short term.
Rarely, it may cause nausea, vomiting, diarrhea, fatigue, headache, and dizziness.
Contaminated algae supplements may cause liver damage, rapid heartbeat, shock, and even death.
There is no reliable information about the use of algae supplements while being pregnant, breastfeeding, or in children.
It is advised to avoid using algae supplements during pregnancy, breastfeeding, and children.
Individuals with autoimmune disorders, weak immune system, bleeding disorders, and phenylketonuria should avoid using algae supplements. Avoid taking algal oil if having low blood pressure.
Possible Drug Interactions of Algae Supplements
Microalgae supplements may decrease the effectiveness of immunosuppressants. Chlorella may decrease the effectiveness of warfarin.    
Dosage of Algae Supplements
There is no recommended dosage of taking algae supplements.
It is a good idea to refer the instructions available on the supplement bottle for dosage.
A standard dose of 1-8 g of spirulina is used to produce a beneficial effect in clinical studies.
Chlorella supplementation in the range of 6-10 g is used in clinical studies.
Astaxanthin is used in the range of 6-8 mg daily.
In recent years, algae supplements have emerged rapidly due to their faster growth and health benefits.
It appears to be beneficial for improving lipid markers, glucose metabolism, reducing inflammation, and lowering oxidative stress.
There remain considerable challenges in quantifying other benefits in humans and determining how algae interact with human physiological processes.
These limitations are to be solved in the with well designed, randomized controlled studies.